Critical 9.1Published Aug 20, 2026

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

Updated under an hour ago (2026-10-19 10:30 UTC)

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It affects cesanta mongoose. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for cesanta mongoose

Exploited in the last 30 days

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.

CVSS: 9.1 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness (CWE): CWE-444
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Aug 20, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

cesanta mongoose cesanta:mongoose (from the name)	before 7.22	CNA record
cesanta mongoose cesanta:mongoose	before 7.22	NVD

References

https://github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6x-refsource-confirm, exploit, vendor-advisory
https://github.com/cesanta/mongoose/pull/3611x-refsource-misc, issue-tracking, patch
https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71x-refsource-misc, patch
https://github.com/cesanta/mongoose/releases/tag/7.22x-refsource-misc, release-notes

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.