CVE-2026-42945: F5 Dos

High severity, CVSS 8.1. EPSS: 3.4% chance of exploitation in the next 30 days.

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module. This vulnerability exists when the rewrite directive is followed by a rewrite, if, or set directive and an unnamed Perl-Compatible Regular Expression (PCRE) capture (for example, $1, $2) with a replacement string that includes a question mark (?). An unauthenticated attacker along with conditions beyond its control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow 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.

Affected products

• F5 Dos: from 4.3.0, up to and including 4.7.0; version 4.8.0 only
• F5 Nginx Gateway Fabric: from 1.3.0, up to and including 1.6.2; from 2.0.0, up to and including 2.5.1
• F5 Nginx Ingress Controller: from 3.5.0, up to and including 3.7.2; from 4.0.0, up to and including 4.0.1; from 5.0.0, up to and including 5.4.1
• F5 Nginx Instance Manager: from 2.16.0, up to and including 2.21.1
• F5 Nginx Open Source: from 0.6.27, up to and including 1.30.0
• F5 Nginx Plus: from r32, up to and including r36
• F5 Waf: from 4.9.0, up to and including 4.16.0; from 5.1.0, up to and including 5.8.0; from 5.9.0, up to and including 5.12.1

Published 2026-05-13. Last modified 2026-09-10.