CVE-2026-42533 — NGINX Map directive and Regex matching vulnerability

Affected: F5 NGINX Plus, F5 NGINX Open Source

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.

USN-8563-1 — nginx vulnerabilities

Affected: Ubuntu:22.04:LTS: nginx, Ubuntu:24.04:LTS: nginx, Ubuntu:26.04:LTS: nginx

It was discovered that nginx incorrectly handled certain map directives using regex matching and capture variables. A remote attacker could use this issue to cause nginx to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-42533)

It was discovered that nginx had a use-after-free vulnerability in the ngx_http_ssi_module module when configured with Server-Side Includes, proxy_pass, and proxy buffering disabled directives. An attacker able to intercept traffic and control responses from an upstream server could possibly use this issue to cause nginx to crash, resulting in a denial of service. (CVE-2026-56434)

It was discovered that nginx incorrectly handled certain requests in the ngx_http_slice_module module. A remote attacker could possibly use this issue to obtain sensitive information or cause nginx to crash, resulting in a denial of service. (CVE-2026-60005)

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CVE-2026-42533 — NGINX Map directive and Regex matching vulnerability

USN-8563-1 — nginx vulnerabilities