CVE-2026-73256: critical vulnerability in cesanta mongoose
Mongoose: HTTP/1.0 detection off-by-one enables request smuggling via chunked TE
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.1epss 0.4%
Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http_cb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mg_http_parse() requires an eight-byte protocol string, so is_http_1_0 is never set. Mongoose consequently processes chunked encoding that an HTTP/1.0 proxy can ignore, enabling request smuggling and unauthorized access or state changes. This issue is fixed in version 7.22.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Affected products
cesanta · mongooseRelated CVEs — cesanta mongoose
In the same product, most dangerous first.
CVE-2026-73257CRITICALMongoose: Content-Length + Transfer-Encoding coexistence enables request smugglingEPSS 0.7%CVE-2026-73255MEDIUMMongoose: Path traversal in SSI #include directives enables arbitrary file readEPSS 0.7%CVE-2026-73258MEDIUMMongoose: Multipart boundary/header scan logic error in mg_http_next_multipartEPSS 0.5%CVE-2026-73261HIGHMongoose: handle_opt() missing opts[1] > len check — 1-byte OOB read corrupts TCP MSS, silences mg_send() per connectionEPSS 0.4%CVE-2026-73259MEDIUMMongoose: Reflected XSS via decoded URI in directory listing renderEPSS 0.4%CVE-2026-73252HIGHMongoose: Unauthenticated remote heap out-of-bounds read in built-in TLS: off-by-one length check in mg_tls_recv_record() underflows recv_len to SIZE_MAXEPSS 0.4%