What’s Vulnerable › Vulnerabilities

CVE-2026-73257: Mongoose: Content-Length + Transfer-Encoding coexistence enables request smuggling

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-08-20 · updated 2026-10-18
• Weakness: CWE-444

Description

Mongoose is an embedded web server and network library. Priro to version 7.22, a remote unauthenticated attacker can send an HTTP request containing both Content-Length and Transfer-Encoding: chunked. The cl_count and te_count checks in the mg_http_parse() and http_cb() paths in src/http.c accept both headers and prioritize chunked encoding, while a Content-Length-preferring reverse proxy can use a different request boundary. This CL.TE desynchronization can inject requests that access or modify resources in another user context. 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-5wfq-r6mr-wqp6
• https://github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6

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