Heap Buffer Overflow in NGINX ngx_http_rewrite_module via PCRE Capture
CVE-2026-42945 Published on May 13, 2026
NGINX ngx_http_rewrite_module vulnerability
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, for systems with Address Space Layout Randomization (ASLR ) disabled, code execution is possible. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Vulnerability Analysis
CVE-2026-42945 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
Heap-based Buffer Overflow
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Products Associated with CVE-2026-42945
stack.watch emails you whenever new vulnerabilities are published in F5 Networks Nginx Plus or F5 Networks Nginx Open Source. Just hit a watch button to start following.
Affected Versions
F5 NGINX Plus:- Version R37 and below * is unaffected.
- Version R36 and below R36 P4 is affected.
- Version R32 and below R32 P6 is affected.
- Version 1.31.0 and below * is unaffected.
- Version 0.6.27 and below 1.30.1 is affected.