What is CVE-2026-42945?
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.
Timeline
- 2026-05-13Published to the U.S. National Vulnerability Database (NVD)
- 2026-05-18First covered in a defend.network daily briefing
- 2026-07-15NVD record last updated
Affected product
F5 Dos
NVD also lists CPE entries for: F5 Dos, F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller, F5 Nginx Instance Manager, F5 Nginx Open Source
Remediation Steps
- Upgrade NGINX to version 1.30.1 or later immediately
- Apply emergency WAF rules to block malformed rewrite module requests
- Monitor worker process logs for abnormal terminations and heap memory patterns
- Implement rate limiting on HTTP requests during patching window
- Validate patches in staging environment prior to production deployment
References
Referenced in our briefings & reports
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