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CVE-2026-58055mediumCWE-444

nghttp2 nghttpx - HTTP Request/Response Smuggling via Upgrade Request with Content-Length

33Vexday Risk Score

No sign of exploitation. It has a public proof of concept.

ssvc Attendcvss 6.3epss 0.3%
exploitation probability
0.3%top 82% of all CVEs
observed exploitation
nono source reports it
1 public exploit(s)
nghttp2's nghttpx proxy through 1.69.0 forwards an HTTP/1.1 Upgrade request that also carries a Content-Length header and body onto reusable keep-alive backend connections, re-adding the Upgrade and Connection headers while passing Content-Length verbatim. A backend that resolves the resulting ambiguous message in the attacker's favor enables HTTP request/response smuggling and cross-client response-queue poisoning.
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:L/SA:N
Affected products
nghttp2 · nghttp2
⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.