Vulnerability in Cesanta Mongoose
CVE-2026-73257
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.
Vulnerability class: HTTP Request Smuggling
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.007 (50.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 50th percentile — 50.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.007 · change: +0.003
Affected products
- Cesanta Mongoose — versions < 7.22
Weakness classification (CWE)
References
- github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6 (Exploit, Vendor Advisory)
- github.com/cesanta/mongoose/pull/3611 (Patch, Issue Tracking)
- github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 (Patch)
- github.com/cesanta/mongoose/releases/tag/7.22 (Release Notes)
Frequently asked questions
- What is CVE-2026-73257?
- CVE-2026-73257 is a critical-severity vulnerability in Cesanta Mongoose, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 9.1/10. Published 2026-08-20.
- How severe is CVE-2026-73257?
- Critical severity. CVSS v3 base score is 9.1 out of 10.