Critical severity · published Aug 20, 2026
CVE-2026-73257
Mongoose: Content-Length + Transfer-Encoding coexistence enables request smuggling
9.1
CVSS
0.7%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.7% · higher than 52% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MO
mongoose · cesanta
< 7.22 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-73257
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-73257
Patch
https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71
Issue Tracking
https://github.com/cesanta/mongoose/pull/3611
Release Notes
https://github.com/cesanta/mongoose/releases/tag/7.22
Exploit
https://github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6
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