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Vulnerability · Published Aug 25, 2026 · Assigned by GitHub_M

CVE-2026-55620eml_parser: DoS via deeply nested parens in Received headers

High 7.5

In plain English

A high-severity resource allocation without limits in eml_parser from GOVCERT-LU. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.6%top 49.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

eml_parser serves as a python module for parsing eml files and returning various information found in the e-mail as well as computed information. Prior to 3.0.2, eml_parser.routing.noparenthesis in eml_parser/routing.py removes parenthesized CFWS comments from Received: headers with a regex-based fix-point loop whose running time is quadratic in the nesting depth. A single Received: header with 5,000 nested parentheses causes approximately 1.3 seconds of CPU saturation per parsed message, and doubling the nesting depth approximately quadruples the running time. An attacker can submit relatively small EML files that consume multiple seconds of processing time, causing worker latency, queue backpressure, and possible service-level outages in synchronous gateways, sandboxes, and real-time triage pipelines. This issue is fixed in version 3.0.2.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPIeml-parser3.0.2GHSA-g7gc-gmgp-wgqg
PyPIeml-parser3.0.2PYSEC-2026-3832

Affected products (as reported)

VendorProductVersions
GOVCERT-LU eml_parser < 3.0.2

Weakness: CWE-770, CWE-1124 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References