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 the root directive or access log format 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. Oct 14, 2026, 2:40 PM UTCCVE published
2. Oct 15, 2026, 3:57 AM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 29, 2026, 4:59 PM UTCRecord last updated

Affected versions

• F5 NGINX Plus

  From 37.1.0 · fixed in 37.1.0.1; From 37.0.0 · fixed in 37.0.5.1; From R36; From R35; From R34; From R33

• F5 NGINX Open Source

  From 1.31.2 · fixed in 1.31.7; From 1.30.0 · fixed in 1.30.6

References 1