CVE-2026-9256
HighCVSS 8.1Exploitation Probability (EPSS)
Very high risk95th percentile - higher than 95% of all known CVEs
Summary
A vulnerability in the ngx_http_rewrite_module of NGINX Plus and NGINX Open Source occurs when a rewrite directive uses a regex pattern with overlapping PCRE captures and a replacement string referencing multiple captures. An unauthenticated attacker can send crafted HTTP requests, causing a heap buffer overflow in the NGINX worker process, leading to a restart.
Risk Assessment
An attacker can cause NGINX worker process crashes (restart) and potentially execute code on systems with ASLR disabled or bypassed.
Recommendation
Update NGINX to a patched version and avoid using regex patterns with overlapping captures in rewrite directives.
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 a rewrite directive uses a regex pattern with distinct, overlapping Perl-Compatible Regular Expression (PCRE) captures (for example, ^/((.*))$) and a replacement string that references multiple such captures (for example, $1$2) in a redirect or arguments context. An unauthenticated attacker along with conditions beyond their 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.