How severe is CVE-2026-58055?

CVE-2026-58055 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-58055 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (10th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-58055?

CVE-2026-58055 affects Nghttp2. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-58055?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2026-58055 published?

CVE-2026-58055 was published on 2026-06-28 and last updated on 2026-06-30.

CVE-2026-58055

CVE-2026-58055 is a medium-severity vulnerability in Nghttp2 with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-444.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
CVSS v4: 6.3
EPSS exploit prediction: 0% (10th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-444
Affected product: Nghttp2
Published: 2026-06-28
Last modified: 2026-06-30

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-58055?: CVE-2026-58055 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-58055 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (10th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-58055?: CVE-2026-58055 affects Nghttp2. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-58055?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2026-58055 published?: CVE-2026-58055 was published on 2026-06-28 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:nghttp2:nghttp2:*:*:*:*:*:*:*:*

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