nghttpx <=1.69.0 HTTP/1.1 Upgrade + Content-Length Smuggling
CVE-2026-58055 Published on June 28, 2026
nghttp2 nghttpx - HTTP Request/Response Smuggling via Upgrade Request with Content-Length
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.
Vulnerability Analysis
CVE-2026-58055 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality and integrity, and no impact on availability.
Weakness Type
What is a HTTP Request Smuggling Vulnerability?
When malformed or abnormal HTTP requests are interpreted by one or more entities in the data flow between the user and the web server, such as a proxy or firewall, they can be interpreted inconsistently, allowing the attacker to "smuggle" a request to one device without the other device being aware of it.
CVE-2026-58055 has been classified to as a HTTP Request Smuggling vulnerability or weakness.
Products Associated with CVE-2026-58055
Want to know whenever a new CVE is published for Nghttp2? stack.watch will email you.
Affected Versions
nghttp2:- Before and including 1.69.0 is affected.