Is CVE-2026-58055 in the CISA KEV catalog?

No. CVE-2026-58055 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-58055?

CVE-2026-58055 has a CVSS v3 base score of 5.4 (Moderate).

What is the EPSS score for CVE-2026-58055?

CVE-2026-58055 has an EPSS score of 0.20% (10th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix or mitigate CVE-2026-58055?

No published fix for CVE-2026-58055 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

CVE & CISA-KEV Catalog

CVE-2026-58055

MEDIUM

5.4

CVSS v3

NVD

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.

CWE-444

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeChanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

Exploit Intelligence

0.20%probability of exploitation in 30 days

10thpercentile

Low risk: more likely to be exploited than 10% of all known CVEs.

References

Patch2

Other references1

github.com

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-30.