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GHSA-G7GC-GMGP-WGQG

Vulnerability from github – Published: 2026-08-25 18:27 – Updated: 2026-08-25 18:27
VLAI
Summary
eml_parser vulnerable to DoS via deeply nested parens in Received headers
Details

Summary

eml_parser strips parenthesised CFWS comments from Received: headers using a regex-based fix-point loop. The loop has quadratic time complexity in the number of nested parens. A single Received: header containing 5,000 nested parens causes ~1.3 seconds of CPU saturation per parsed message; runtime quadruples per doubling of nesting depth.

Impact

This represents a CPU exhaustion DoS in any pipeline that processes attacker-supplied EML files. An attacker can create relatively small EML files that will take multiple seconds to parse.

This is particularly problematic for synchronous email-processing pipelines (gateways, sandboxes, real-time triage) where worker latency directly translates to queue backpressure and possible service-level outages.

Patches

Since version 3.0.2, eml_parser uses a linear-time algorithm to remove the comments from Received: headers.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "eml_parser"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.0.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55620"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770",
      "CWE-1124"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-25T18:27:18Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\n`eml_parser` strips parenthesised CFWS comments from `Received:` headers using a regex-based fix-point loop. The loop has quadratic time complexity in the number of nested parens. A single `Received:` header containing 5,000 nested parens causes ~1.3 seconds of CPU saturation per parsed message; runtime quadruples per doubling of nesting depth.\n\n### Impact\n\nThis represents a CPU exhaustion DoS in any pipeline that processes attacker-supplied EML files. An attacker can create relatively small EML files that will take multiple seconds to parse.\n\nThis is particularly problematic for synchronous email-processing pipelines (gateways, sandboxes, real-time triage) where worker latency directly translates to queue backpressure and possible service-level outages.\n\n### Patches\n\nSince version 3.0.2, `eml_parser` uses a linear-time algorithm to remove the comments from `Received:` headers.",
  "id": "GHSA-g7gc-gmgp-wgqg",
  "modified": "2026-08-25T18:27:18Z",
  "published": "2026-08-25T18:27:18Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/GOVCERT-LU/eml_parser/security/advisories/GHSA-g7gc-gmgp-wgqg"
    },
    {
      "type": "WEB",
      "url": "https://github.com/GOVCERT-LU/eml_parser/pull/90"
    },
    {
      "type": "WEB",
      "url": "https://github.com/GOVCERT-LU/eml_parser/commit/746a69f86443eb0b6a47f77db3cfe727c21f92b3"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/GOVCERT-LU/eml_parser"
    },
    {
      "type": "WEB",
      "url": "https://github.com/GOVCERT-LU/eml_parser/releases/tag/v3.0.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "eml_parser vulnerable to DoS via deeply nested parens in Received headers"
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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