NGINX Map directive and Regex matching vulnerability

Summary

A vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex matching and a string expression references the map's regex capture variables before referencing the map output variable. Alternatively, the same result could be achieved by using a non-cacheable variable in a string expression under certain conditions. 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. Impact: This vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to possibly trigger a code execution. There is no control plane exposure; this is a data plane issue only.  Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Timeline

1. Jul 15, 2026, 12:00 AM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: total

2. Jul 15, 2026, 2:33 PM UTCCVE published
3. Jul 29, 2026, 3:55 AM UTCRecord last updated

Affected versions

• F5 NGINX Plus

  From 37.0.0.1 · fixed in 37.0.3.1; From R36 · fixed in R36 P7; From R33

• F5 NGINX Open Source

  From 1.31.2 · fixed in 1.31.3; From 0.9.6 · fixed in 1.30.4

References 13