What’s Vulnerable › Vulnerabilities

CVE-2026-73258: Mongoose: Multipart boundary/header scan logic error in mg_http_next_multipart

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-08-20 · updated 2026-10-18
• Weakness: CWE-697

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.

Affected products

• Cesanta Mongoose: before 7.22 — fixed in 7.22

How to fix

Upgrade to a fixed version: Cesanta Mongoose 7.22. Check the vendor advisory for mitigations.

References

• https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71
• https://github.com/cesanta/mongoose/pull/3611
• https://github.com/cesanta/mongoose/releases/tag/7.22
• https://github.com/cesanta/mongoose/security/advisories/GHSA-cc55-8v3r-59p8
• https://github.com/cesanta/mongoose/security/advisories/GHSA-cc55-8v3r-59p8

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