CVE-2026-73257: CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in cesanta mongoose
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 v3.1
Score 9.1critical
Affected software
cesanta
mongoose
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-73257 is an HTTP request smuggling vulnerability in cesanta mongoose prior to version 7.22. The vulnerability occurs because the mg_http_parse() and http_cb() functions in src/http.c accept both Content-Length and Transfer-Encoding: chunked headers and prioritize chunked encoding. However, a reverse proxy that prefers Content-Length can interpret the request boundaries differently, causing a desynchronization between the proxy and the server. This desynchronization enables an attacker to inject HTTP requests that can access or modify resources belonging to other users. This vulnerability is classified under CWE-444 (Inconsistent Interpretation of HTTP Requests).
Potential Impact
An unauthenticated remote attacker can exploit this vulnerability to inject HTTP requests that may access or modify resources in another user's context. This can lead to unauthorized data access and modification, compromising confidentiality and integrity. The CVSS v3.1 score is 9.1 (critical), reflecting the high impact on confidentiality and integrity with no required privileges or user interaction.
Mitigation Recommendations
This vulnerability is fixed in mongoose version 7.22. Users should upgrade to version 7.22 or later to remediate this issue. No other mitigation or temporary workaround is indicated in the provided data. Patch status is not explicitly confirmed beyond the fix in version 7.22; users should verify with the vendor advisory for the latest remediation guidance.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-11T17:18:01.598Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a873eeeacd9273b49f2b5e8
Added to database: 08/20/2026, 17:52:46 UTC
Last enriched: 08/20/2026, 18:07:09 UTC
Last updated: 10/04/2026, 18:53:18 UTC
Views: 68
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