UBUNTU-CVE-2026-42533

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UBUNTU-CVE-2026-42533

Summary:

Details: 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.

References: https://ubuntu.com/security/CVE-2026-42533, https://www.cve.org/CVERecord?id=CVE-2026-42533, https://my.f5.com/manage/s/article/K000162097, https://cyberstan.co.uk/nginx-rce/, https://github.com/imbas007/cve-2026-42533, https://ubuntu.com/security/notices/USN-8563-1, https://ubuntu.com/security/notices/USN-8563-2, https://ubuntu.com/security/notices/USN-8563-3, https://ubuntu.com/security/notices/USN-8563-4, https://ubuntu.com/security/notices/USN-8563-5, https://ubuntu.com/security/notices/USN-8955-2