CVE-2026-58055
MediumCVSS 5.4Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
A vulnerability in nghttp2 nghttpx up to version 1.69.0 causes an HTTP/1.1 Upgrade request with a Content-Length header and body to be forwarded onto reusable keep-alive backend connections. A backend interpreting this ambiguous message in the attacker's favor enables HTTP request/response smuggling and cross-client response-queue poisoning.
Risk Assessment
An attacker can exploit this vulnerability to intercept or modify traffic between clients and the backend, leading to confidentiality and integrity breaches and potential attacks on other users.
Recommendation
It is recommended to immediately upgrade nghttp2 to a version later than 1.69.0, which includes a fix that prevents improper forwarding of Upgrade requests with a Content-Length header.
Other vulnerabilities in nghttp2
See all- CVE-2024-28182Medium
The nghttp2 library prior to version 1.61.0 keeps reading an unbounded number of HTTP/2 CONTINUATION frames even after a stream is reset to keep the HPACK context in sync. This causes excessive CPU usage to decode HPACK state.
- CVE-2015-8659Critical
Idle stream handling in nghttp2 before version 1.6.0 contains a heap-use-after-free bug that can be exploited by attackers in unspecified ways.
- CVE-2026-24029Medium
When the early_acl_drop (earlyACLDrop in Lua) option is disabled (default is enabled) on a DNS over HTTPS frontend using the nghttp2 provider, the ACL check is skipped, allowing all clients to send DoH queries regardless of the configured ACL.
- CVE-2026-27135High
In nghttp2 library before version 1.68.1, missing internal state validation after calling `nghttp2_session_terminate_session` or `nghttp2_session_terminate_session2` causes the library to continue reading incoming data. Receiving a malformed frame can trigger an assertion failure and crash.
Original NVD description (English source)
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.