CVE-2026-42533

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.

Score

CVSS 4.0 9.2 Critical

Status

Analyzed - f5sirt@f5.com

Published

2026-07-15

Last modified

2026-07-29

Weaknesses

CWE-122

Affected products

• Nginx Gateway Fabric (F5)
• Nginx Ingress Controller (F5)
• Nginx Open Source (F5)
• Nginx Plus (F5)
• Waf (F5)

References

• https://my.f5.com/manage/s/article/K000162097