CVE-2026-42533

What is 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.

Timeline

• 2026-07-15Published to the U.S. National Vulnerability Database (NVD)
• 2026-07-16NVD record last updated
• 2026-07-20First covered in a defend.network daily briefing

Affected product

See advisory

References

• https://my.f5.com/manage/s/article/K000162097
• https://nvd.nist.gov/vuln/detail/CVE-2026-42533

Referenced in our briefings & reports

• Vulnerability Priority Report – Week 3 of July 2026 (July 20 – 26)
• NGINX, WordPress, SonicWall RCEs under active exploitation; patched versions released (2026-07-20)