CVE-2026-42533

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.

• CVE-2026-42533-POCExploit

  CVE-2026-42533: pre-auth nginx heap overflow and info leak from PCRE capture clobbering in the map/script engine, chained to RCE.

• ghostlock-vagrant-boxResearch

  An isolated Vagrant testbed designed to simulate a complete attack chain: Initial access via the Nginx heap buffer overflow (CVE-2026-42533) followed by root privilege escalation using the Ghostlock kernel vulnerability (CVE-2026-43449).