eml_parser has parser DoS via deeply nested parentheses in e-mail headers

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-55619: 0.52% estimated exploitation activity in the next 30 days; percentile 44.47 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary emlparser uses the email.utils.getaddresses() function from the CPython standard library to parse e-mail headers that contain e-mail addresses (such as To, Cc, Bcc, From, Reply-To, Sender, ...). When the input header contains a deeply nested CFWS (comment / folding white space) construct, the recursive descent parser in the standard library exhausts the call stack. The resulting RecursionError is not caught by emlparser, so the exception propagates and aborts parsing of the whole message. Impact SOC pipelines use emlparser to process untrusted e-mails. An attacker can easily create an eml file that will trigger the RecursionError during parsing. The impact is mitigated by the fact that there are various other situations in which emlparser will raise an exception when attempting to parse a malformed or pathological eml file. In particular, very deeply nested multipart e-mails also result in a RecursionError being raised by the library voluntarily. Therefore, systems relying on…

Published by the source

25 Aug 2026, 18:25 UTC

Last modified by the source

25 Aug 2026, 18:25 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-m66c-fw79-6359

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# Patch Next advisory brief: CVE-2026-55619

Advisory: eml_parser has parser DoS via deeply nested parentheses in e-mail headers
IDs: CVE-2026-55619, GHSA-m66c-fw79-6359
Record: https://patchnext.com/advisories/cve-2026-55619 (revision 1, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: eml-parser 3.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI eml-parser: affected < 3.0.2; fixed in 3.0.2

## Suggested inspection (read-only)
- `python -m pip show eml-parser`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on eml-parser.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-m66c-fw79-6359 (GitHub-reviewed advisory GHSA-m66c-fw79-6359 lists affected ranges: PyPI eml-parser >=0 <3.0.2)

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