CVE-2026-58055

EUVD-2026-39975

28.06.2026, 02:16

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.

HTTP Request/Response Smuggling

Provider	Type	Base Score	Atk. Vector	Atk. Complexity	Priv. Required	Vector
VulnCheck	CNA	5.4 MEDIUM	NETWORK	HIGH	NONE	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

Base Score

CVSS 3.x

EPSS Score

Percentile: 10%

Early Detection

Affected products identified ahead of NVD analysis through intelligence sources.

Vendor	Product	Version	Source
nghttp2	nghttp2	𝑥 ≤ 1.69.0	CNA

Debian Releases

Debian Product

Codename

nghttp2

bookworm	vulnerable
bookworm (security)	vulnerable
bullseye	vulnerable
bullseye (security)	vulnerable
forky	vulnerable
sid	vulnerable
trixie	vulnerable
trixie (security)	vulnerable

Common Weakness Enumeration

CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

References

https://github.com/bikini/exploitarium/tree/main/nghttp2-nghttpx-upgrade-queue-poison-poc

https://github.com/nghttp2/nghttp2/commit/ab28105c4a0197da24f8bfc414bc116055249e1e

https://www.vulncheck.com/advisories/nghttp2-nghttpx-http-request-response-smuggling-via-upgrade-request-with-content-length