CVE-2026-58055: nghttp2's nghttpx proxy through 1.69.0 forwards an HTTP/1.1 Upgrade request that also carries a Content-Length

Q: How do I fix CVE-2026-58055?

nghttp2: upgrade to newer than 1.69.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-58055 being exploited?

CVE-2026-58055 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-58055 affect?

CVE-2026-58055 affects nghttp2. Severity is medium (CVSS 5.4). 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-

Q: How urgent is CVE-2026-58055?

Priority 28/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.4REMOTEUPGRADE

CVE-2026-58055 is a medium-severity flaw (CVSS 5.4) affecting nghttp2. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 83%)
CISA exploited list	No
Weakness	CWE-444
Published	2026-06-28
Last modified	2026-10-25

Publisher (CNA): VulnCheck · Vendor: nghttp2

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-28 02:16 UTCPublished CVE record published
2026-10-25 17:10 UTCUpdated Record last modified

nghttp2 nghttp2 UPGRADE

Affected: <= 1.69.0

Fixed in: newer than 1.69.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy nghttp2 || rpm -q nghttp2 || nghttp2 --version

2. UPGRADE to newer than 1.69.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nghttp2

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nghttp2

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-58055?

nghttp2: upgrade to newer than 1.69.0. Exact commands for each OS are on this page.

Is CVE-2026-58055 being exploited?

CVE-2026-58055 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-58055 affect?

CVE-2026-58055 affects nghttp2. Severity is medium (CVSS 5.4). 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-

How urgent is CVE-2026-58055?

Priority 28/100. Remotely exploitable, no login, no user action

References

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