{"id":"CVE-2026-55620","aliases":["GHSA-g7gc-gmgp-wgqg","PYSEC-2026-3832"],"url":"https://o3.security/vulnerability/CVE-2026-55620","summary":"eml_parser: DoS via deeply nested parens in Received headers","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.","published":"2026-08-25T18:26:54.978Z","modified":"2026-09-11T03:30:41.796504841Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00366,"percentile":0.29373,"asOf":"2026-08-27"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"eml-parser","fixedVersion":"3.0.2"}],"fix":{"url":"https://github.com/GOVCERT-LU/eml_parser/commit/746a69f86443eb0b6a47f77db3cfe727c21f92b3","label":"GOVCERT-LU/eml_parser@746a69f"},"references":[{"type":"WEB","url":"https://github.com/GOVCERT-LU/eml_parser/releases/tag/v3.0.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55620.json"},{"type":"ADVISORY","url":"https://github.com/GOVCERT-LU/eml_parser/security/advisories/GHSA-g7gc-gmgp-wgqg"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55620"},{"type":"FIX","url":"https://github.com/GOVCERT-LU/eml_parser/commit/746a69f86443eb0b6a47f77db3cfe727c21f92b3"},{"type":"FIX","url":"https://github.com/GOVCERT-LU/eml_parser/pull/90"},{"type":"PACKAGE","url":"https://github.com/GOVCERT-LU/eml_parser"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-11T03:30:41.796504841Z"}}