CVE-2026-58055: nghttp2 nghttpx - HTTP Request/Response Smuggling via Upgrade Request with Content-Length

mediumCVSS 5.4CVE-2026-58055

CSIRTS triage

product: nghttp2Other

What: HTTP request/response smuggling can occur via an Upgrade Request with Content-Length in nghttp2 nghttpx.
Who is affected: Deployments using nghttp2 nghttpx.
Urgency: Remediation is medium priority as it could lead to unexpected behavior but is not actively exploited.
Action: Update nghttp2 to the latest version to mitigate the issue.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 5.4
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-58055

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-580550.20% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 10% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-58055	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for nghttp2 nghttpx -

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-58055: nghttp2's nghttpx proxy through 1.69.0 forwards an HTTP/1.1 Upgrade request that also carries …nvd · 2026-06-28