Mongoose: Multipart boundary/header scan logic error in mg_http_next_multipart

Description

Mongoose is an embedded web server and network library. Prior to 7.22, a remote attacker can place a lone carriage return or line feed in multipart input processed by mg_http_next_multipart() in src/http.c. The loops comparing s[b] and s[b + 1], and s[h2] and s[h2 + 1], use an incorrect AND condition and stop when either character resembles part of a CRLF terminator. This truncates headers, filenames, or boundaries and can cause an application to accept dangerous content after seeing a misleading Content-Type value. This issue is fixed in version 7.22.

Scores

EPSS (exploitation in 30 days)

0.46% · top 60% of all CVEs (6 Nov 2026)

CISA SSVC

Exploitation: poc · Automatable: yes · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.5.

Weakness

• CWE-697: Incorrect Comparison (opens in a new tab)All about CWE-697 and its CVEs

Affected products

• cesanta · mongoose

  • affected < 7.22

References (4)

• https://github.com/cesanta/mongoose/security/advisories/GHSA-cc55-8v3r-59p8 (opens in a new tab)x_refsource_CONFIRMexploit
• https://github.com/cesanta/mongoose/pull/3611 (opens in a new tab)x_refsource_MISC
• https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 (opens in a new tab)x_refsource_MISC
• https://github.com/cesanta/mongoose/releases/tag/7.22 (opens in a new tab)x_refsource_MISC

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-73258](https://trackcve.app/badge/CVE-2026-73258.svg)](https://trackcve.app/cve/CVE-2026-73258)

Record last updated 20 Aug 2026, 18:32 UTC.