Quick answers
- Is CVE-2026-9256 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-9256 being exploited in the wild.
- How severe is CVE-2026-9256?
- High severity, with a CVSS score of 8.1, published 22 May 2026.
- Which products and versions are affected?
- F5 Nginx Plus r32-r36, 37.0.0-37.0.1.0.
- Is there a fix for CVE-2026-9256?
- A patch was published on 2026-05-22: Fixed in NGINX 1.31.1 and 1.30.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-9256 attacked?
- It is attacked over the network, in a hosted service.
- Am I affected by CVE-2026-9256?
- Check whether you run F5 Nginx Plus at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A heap-based buffer overflow exists in the ngx_http_rewrite_module of NGINX. The flaw is triggered when a rewrite directive uses a regular expression with overlapping PCRE captures (e.g., ^/((.*))$) and a replacement string that references multiple such captures (e.g., $1$2) within a redirect or arguments context. An unauthenticated remote attacker can exploit this by sending crafted HTTP requests, leading to a worker process crash (DoS). If Address Space Layout Randomization (ASLR) is disabled or bypassed, arbitrary code execution may be possible. The issue is fixed in NGINX Open Source versions 1.31.1 and 1.30.2, and NGINX Plus version 37.0.1.1.
Affected products
- F5 NGINX Plus r32-r36, 37.0.0-37.0.1.0
- F5 NGINX Open Source 0.1.17-0.9.7, 1.0.0-1.30.1, 1.31.0
Timeline
- 2026-05-22: disclosed
- 2026-05-22: advisory
- 2026-05-22: patched: Fixed in NGINX 1.31.1 and 1.30.2