Critical [CVE-2026-42533] 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
This critical-severity F5 advisory covers CVE-2026-42533 affecting NGINX Plus, NGINX Open Source.
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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.
- NGINX Plus 37.0.0.1 before 37.0.3.1
- NGINX Plus R36 before R36 P7
- NGINX Plus R33
- NGINX Open Source 1.31.2 before 1.31.3
- NGINX Open Source 0.9.6 before 1.30.4
Official advisory · high-confidence parse· fetched 4 months ago·verify at source
- 37.0.3.1
- R36 P7
- 1.31.3
- 1.30.4
Official advisory · high-confidence parse· fetched 4 months ago·verify at source
Mitigation
Upgrade to a fixed release: 37.0.3.1, R36 P7, 1.31.3, 1.30.4. That is the remediation for this advisory.
The vendor advisory may list interim mitigations or workarounds not captured here. Review it before change work.
Official advisory · high-confidence parse· fetched 4 months ago·verify at source
More F5 advisories
- CVE-2026-95101Oct 14, 2026Description NGINX Plus and NGINX Open Source have a vulnerability
- CVE-2026-97205Oct 14, 2026NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_core_module module
- CVE-2026-93479Oct 14, 2026vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex
- CVE-2026-97629Oct 14, 2026Description When NGINX Plus or NGINX Open Source is configured with ssl_session_cache
- CVE-2026-15176Oct 14, 2026vulnerability exists in NGINX Plus and NGINX Open Source when a location is configured
- CVE-2026-90439Sep 15, 2026NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_v3_module module
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