Critical [CVE-2026-9256] NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module
This critical-severity F5 advisory covers CVE-2026-9256 affecting NGINX Plus, NGINX Open Source.
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Summary
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.
- NGINX Plus 37.0 before 37.0.1.1
- NGINX Plus R36 before R36 P5
- NGINX Plus R32 before R32 P7
- NGINX Open Source 1.31.0 before 1.31.1
- NGINX Open Source 1.30.0 before 1.30.2
- NGINX Open Source 0.1.17 through 0.9.7
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
- 37.0.1.1
- R36 P5
- R32 P7
- 1.31.1
- 1.30.2
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
Mitigation
Upgrade to a fixed release: 37.0.1.1, R36 P5, R32 P7, 1.31.1, 1.30.2. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 1 month ago·verify at source
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