CVE-2026-42533 remediation guide
F5 NGINX Plus, 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...
A verified fixed-version field is not available. Use the linked NVD and supporting references, then confirm the vendor-supported path before changing production systems.
Identify the affected asset
Confirm whether F5 NGINX Plus, NGINX Open Source is installed, record the deployed version and installation path, and identify exposed interfaces.
- Record the product name, package or appliance identifier, and installed version.
- Identify internet-facing, administrative, API, and internal access paths.
- Preserve the pre-change configuration and relevant service logs.
Validate the affected-version match
Compare the deployed version with the affected range: >= 37.0.0.1 < 37.0.3.1, >= R36 < R36 P7, >= R33, >= 1.31.2 < 1.31.3, >= 0.9.6 < 1.30.4. Treat incomplete inventory results as unresolved.
Prioritize with independent signals
The CVSS severity warrants an early asset and exposure review. Combine this signal with asset criticality, exposure, compensating controls, and business impact.
Apply supported remediation
Follow the vendor advisory or supported update path. Current fixed-version status: No verified fixed-version field is available yet. Preserve configuration and rollback material before change.
Verify the result
Confirm the resulting version, service health, authentication and access paths, monitoring coverage, and relevant security logs.
- Confirm the expected version and package state.
- Run a functional health check for critical service paths.
- Review authentication, error, application, and security monitoring logs.
- Reassess exposure if the supported fix cannot be applied.
Operational boundary
This page does not replace the vendor advisory, support contract, change-management process, or recovery plan. Do not infer that an asset is unaffected from an incomplete inventory query or a missing fixed-version field.