Use After Free in F5 nginx Gateway Fabric

CVE-2026-42530

NGINX Open Source has a vulnerability in the ngx_http_v3_module module. When NGINX Open Source is configured to use the HTTP/3 QUIC module, a remote unauthenticated attacker along with conditions beyond their control can use a specially crafted HTTP/3 session to reopen a QPACK encoder stream. This may cause a Use-after-Free in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Vulnerability class: Use-After-Free

Published · last modified .

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.062 (93.5th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 94th percentile — 93.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-42530: rose from 0.011 to 0.062.

EPSS over last 30 days · oldest: 0.011 · newest: 0.062 · change: +0.051

Affected products

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-42530?
CVE-2026-42530 is a high-severity vulnerability in F5 nginx Gateway Fabric, classified under Use After Free. CVSS score: 8.1/10. Published 2026-06-17.
How severe is CVE-2026-42530?
High severity. CVSS v3 base score is 8.1 out of 10.
Is CVE-2026-42530 known to be exploited?
5 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.