Vulnerability-Lookup

GHSA-3M7F-6HXV-6796

Vulnerability from github – Published: 2026-08-27 18:32 – Updated: 2026-08-27 18:32

Details

NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.

Severity

3.7 (Low)


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

6.3 (Medium)


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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-81725"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-27T17:21:03Z",
    "severity": "MODERATE"
  },
  "details": "NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.",
  "id": "GHSA-3m7f-6hxv-6796",
  "modified": "2026-08-27T18:32:30Z",
  "published": "2026-08-27T18:32:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-8mpw-7fpc-4gqj"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81725"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-before-3.10.3-regular-expression-denial-of-service-via-pl196xcorpusreader"
    }
  ],
  "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:L",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/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"
    }
  ]
}

CVE-2026-81725 (GCVE-0-2026-81725)

Vulnerability from cvelistv5 – Published: 2026-08-27 14:51 – Updated: 2026-08-28 15:58

Title

NLTK before 3.10.3 Regular Expression Denial of Service via Pl196xCorpusReader

Summary

Severity

6.3 (Medium)


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

3.7 (Low)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-27 18:24 UTC

CWE

CWE-400 - Uncontrolled Resource Consumption

Assigner

VulnCheck mitre root

References

2 references

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

Impacted products

1 product

Vendor	Product	Version
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

Show details on NVD website

JSON

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{
  "containers": {
    "adp": [
      {
        "metrics": [
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            "other": {
              "content": {
                "id": "CVE-2026-81725",
                "options": [
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                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-27T18:24:00.717908Z",
                "version": "2.0.3"
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              "versionType": "semver"
            }
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      ],
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        },
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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.

Action not permitted

GHSA-3M7F-6HXV-6796

CVE-2026-81725 (GCVE-0-2026-81725)

Tags

Sightings

Nomenclature