CVE-2026-42530: NGINX Open-Source ngx_http_v3_module vulnerability

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of 29 Oct 2026. If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?

6.5%

Up from 1.5% on 22 Oct 2026.

EPSS score, percentile 93.7 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

9.2 Critical

CVSS v4.0 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (1)

Which versions are affected?

Affected

• from 1.31.0 to before 1.31.2

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 29 Oct 2026. About the data.

What to do

Advisories and patches

• my.f5.com (Vendor advisory)

This summary is based on the CVE record as of 29 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Versions not listed are: unknown.

Source: CVE List, as of 29 Oct 2026. About the data.

About this vulnerability

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…

Summary: CVE record, as of 29 Oct 2026.

• CISA has not added CVE-2026-42530 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
• The CVE record was published on 17 Jun 2026.
• The CVE record carries a CVSS v4.0 base score of 9.2 (Critical), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 6.5% (percentile 93.7), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
• CISA's SSVC assessment in the CVE record: exploitation none, automatable no, technical impact total.
• The credits in the CVE record name OpenAI as finder.

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; CVE List, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026. About the data.

Description

NGINX Open-Source ngx_http_v3_module vulnerability

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.

Source: CVE List, as of 29 Oct 2026. About the data.

Timeline

Known exploited F5 vulnerabilities

• CVE-2026-94127: F5 BIG-IP APM Heap-based Buffer Overflow Vulnerability (added 22 Sep 2026)
• CVE-2025-53521: F5 BIG-IP Stack-Based Buffer Overflow Vulnerability (added 27 Mar 2026)
• CVE-2023-46747: F5 BIG-IP Configuration Utility Authentication Bypass Vulnerability (added 31 Oct 2023)
• CVE-2023-46748: F5 BIG-IP Configuration Utility SQL Injection Vulnerability (added 31 Oct 2023)
• CVE-2022-1388: F5 BIG-IP Missing Authentication Vulnerability (added 10 May 2022)