Vulnerability in Nghttp2
CVE-2026-58055
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.
Vulnerability class: HTTP Request Smuggling
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (22.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 22nd percentile — 22.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.001
Affected products
- Nghttp2 — versions 0
Weakness classification (CWE)
References
- github.com/bikini/exploitarium/tree/main/nghttp2-nghttpx-upgrade-queue-poison-p… (exploit, Broken Link, third-party-advisory)
- github.com/nghttp2/nghttp2/commit/ab28105c4a0197da24f8bfc414bc116055249e1e (Patch, patch)
- www.vulncheck.com/advisories/nghttp2-nghttpx-http-request-response-smuggling-vi… (Patch, Third Party Advisory, third-party-advisory)
Frequently asked questions
- What is CVE-2026-58055?
- CVE-2026-58055 is a medium-severity vulnerability in Nghttp2, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.4/10. Published 2026-06-28.
- How severe is CVE-2026-58055?
- Medium severity. CVSS v3 base score is 5.4 out of 10.