Executive brief
NGINX Plus and NGINX Open Source are widely used web servers and load balancers. A vulnerability in how these servers process specific configuration rules could allow an unauthenticated attacker to crash the server or potentially take control of the system. This could lead to website downtime or the theft of sensitive data handled by the server.
Technical details
A heap-based buffer overflow (CWE-122) exists in NGINX Plus and NGINX Open Source when the 'map' directive uses regular expression matching. The vulnerability is triggered when a string expression references the map's regex capture variables before referencing the map output variable, or when using non-cacheable variables under specific conditions. An unauthenticated remote attacker can exploit this by sending specially crafted HTTP requests. Successful exploitation can cause the NGINX worker process to crash (DoS) or allow for arbitrary code execution, particularly on systems where ASLR is disabled or can be bypassed. The issue is confined to the data plane.
Affected products
- F5 NGINX Plus R33, R36 before R36 P7, 37.0.0.1 before 37.0.3.1
- F5 NGINX Open Source 0.9.6 before 1.30.4, 1.31.2 before 1.31.3
Timeline
- 2026-07-15: advisory: F5 published the security advisory K000162097
- 2026-07-15: disclosed: CVE-2026-42533 published to NVD