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Description

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.

PUBLISHED Reserved 2026-06-28 | Published 2026-06-28 | Updated 2026-06-28 | Assigner VulnCheck




MEDIUM: 5.4CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
MEDIUM: 6.3CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:L/SA:N

Problem types

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Product status

Default status
affected

Any version
affected

Credits

ashdfrkl finder

References

github.com/.../main/nghttp2-nghttpx-upgrade-queue-poison-poc (Proof of Concept) exploit third-party-advisory

github.com/...ommit/ab28105c4a0197da24f8bfc414bc116055249e1e (Fix commit (master)) patch

www.vulncheck.com/...via-upgrade-request-with-content-length (VulnCheck Advisory: nghttp2 nghttpx - HTTP Request/Response Smuggling via Upgrade Request with Content-Length) third-party-advisory

cve.org (CVE-2026-58055)

nvd.nist.gov (CVE-2026-58055)

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