CVE-2026-124016
postal-mime < 4.2.1 Algorithmic Complexity DoS via processLine
postal-mime before 4.2.1 contains an algorithmic complexity denial of service vulnerability that allows unauthenticated remote attackers to cause excessive CPU consumption in the PostalMime.processLine() function by crafting deeply nested multipart email messages with boundary lines sharing long prefixes with open boundaries. Attackers can deliver a malicious email with nesting up to the default maxNestingDepth of 256, causing per-line parsing cost to scale as O(depth x shared prefix length) and blocking the Node.js event loop for seconds per message.
Fixes and workarounds
Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: VulnCheckAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| postal-mime postalsys postal-mime
npm |
≥ 0; < 4.2.1 (affected, semver)
Other versions: unaffected |
CNA: VulnCheck |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 4.0 / 6.9 medium |
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N | CNA: VulnCheck |
| 3.1 / 5.3 medium |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L | CNA: VulnCheck |
Exploit evidence
- https://github.com/postalsys/postal-mime/security/advisories/GHSA-q8wm-54mj-r36p
exploit · ADP: CISA-ADP
References
- https://github.com/postalsys/postal-mime/security/advisories/GHSA-q8wm-54mj-r36pCNA: VulnCheck · vendor-advisory
- https://github.com/postalsys/postal-mime/releases/tag/v4.2.1CNA: VulnCheck · release-notes, patch
- https://www.vulncheck.com/advisories/postal-mime-algorithmic-complexity-dos-via-processlineCNA: VulnCheck · third-party-advisory
- https://github.com/postalsys/postal-mime/security/advisories/GHSA-q8wm-54mj-r36pADP: CISA-ADP · exploit
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