Bug 2520646 (CVE-2026-73257)

Summary: CVE-2026-73257 mongoose: Mongoose: Content-Length + Transfer-Encoding coexistence enables request smuggling
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: urgent    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Mongoose. When processing incoming requests containing both Content-Length and Transfer-Encoding headers, the server accepts both headers instead of rejecting the malformed request. In environments where an upstream proxy processes request boundaries differently, a remote, unauthenticated attacker can exploit this discrepancy to perform HTTP request smuggling. This allows an attacker to bypass front-end controls and access or alter sensitive data belonging to other users.
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Bug Depends On: 2538593    
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Description OSIDB Bzimport 2026-08-20 17:56:09 UTC 
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.