Vulnerability Description
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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| F5 | Nginx Open Source | >= 0.1.17, <= 0.9.7 |
| F5 | Nginx Plus | >= r33, < r36 |
| F5 | Dos | >= 4.3.0, <= 4.7.0 |
| F5 | Nginx Gateway Fabric | >= 1.3.0, <= 1.6.2 |
| F5 | Nginx Ingress Controller | >= 3.5.0, <= 3.7.2 |
| F5 | Nginx Instance Manager | >= 2.17.0, < 2.22.1 |
| F5 | Waf | >= 4.10.0, <= 4.16.0 |
| Redhat | Discovery | - |
| Redhat | Hardened Images | - |
| Redhat | Update Infrastructure | >= 5.0, < 5.2 |
| Debian | Debian Linux | 11.0 |
| Redhat | Enterprise Linux | 8.0 |
Related Weaknesses (CWE)
References
- https://my.f5.com/manage/s/article/K000161377MitigationVendor Advisory
- http://www.openwall.com/lists/oss-security/2026/05/22/14Mailing List
- https://lists.debian.org/debian-lts-announce/2026/06/msg00023.htmlMailing ListThird Party Advisory
- https://access.redhat.com/errata/RHSA-2026:20351Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:28212Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:28921Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:28973Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:29151Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:29874Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:33313Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:44481Third Party Advisory
- https://access.redhat.com/security/cve/CVE-2026-9256Third Party Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2480746Issue TrackingThird Party Advisory
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-9256.jsonThird Party Advisory
FAQ
What is CVE-2026-9256?
CVE-2026-9256 is a vulnerability with a CVSS score of 8.1 (HIGH). 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-Com...
How severe is CVE-2026-9256?
CVE-2026-9256 has been rated HIGH with a CVSS base score of 8.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-9256?
Check the references section above for vendor advisories and patch information. Affected products include: F5 Nginx Open Source, F5 Nginx Plus, F5 Dos, F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller.