CVE-2026-42945
HighCVSS 8.1Exploitation Probability (EPSS)
Very high risk99th percentile - higher than 99% of all known CVEs
Summary
A vulnerability exists in NGINX Plus and NGINX Open Source within the ngx_http_rewrite_module. It occurs when the rewrite directive is followed by rewrite, if, or set directives and an unnamed PCRE capture (e.g., $1, $2) with a replacement string containing a question mark (?). An unauthenticated attacker can send crafted HTTP requests, causing a heap buffer overflow in the NGINX worker process, leading to a restart.
Risk Assessment
This vulnerability allows remote code execution on systems with ASLR disabled or when the attacker can bypass ASLR. It could lead to full compromise of the NGINX server and potentially the underlying system.
Recommendation
Immediately update NGINX to the latest patched version. Enable ASLR on the operating system and consider additional security measures such as a web application firewall.
Original NVD description (English source)
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.