Buffer overflow in F5 Nginx Open Source
CVE-2026-9256
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) captu…
Vulnerability class: Buffer Overflow
EPSS: 0.002 (47.0th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
Affected products
- F5 Nginx Open Source — versions 1.31.0, 1.30.0, 0.1.17
- F5 Nginx Plus — versions 37.0, R36, R32
Weakness classification (CWE)
Public proof-of-concept exploits
References
- f5sirt@f5.com (vendor-advisory)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2026-9256?
- CVE-2026-9256 is a high-severity vulnerability in F5 Nginx Open Source, classified under Heap-based Buffer Overflow. CVSS score: 8.1/10. Published 2026-05-22.
- How severe is CVE-2026-9256?
- High severity. CVSS v3 base score is 8.1 out of 10.
- Is CVE-2026-9256 known to be exploited?
- 4 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.