CVE-2026-58055

Medium

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.

SeverityMedium

CVSS5.4

Exploit probability—

ProductNghttp2

PublishedJun 28, 2026

First seenJun 28, 2026

Weakness typeCWE-444CWE-444

How to fix

Patches

github.com/nghttp2/nghttp2/commit/ab28105c4a0197da24f8bfc414bc116055249e1e

Affected products

Product	Affected versions	Fixed in
nghttp2 nghttp2	v ≤ 1.69.0	—

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