CVE-2026-40701

A flaw was found in the ngx_http_ssl_module module of NGINX. When the ssl_verify_client directive is set to "on" or "optional" and the ssl_ocsp directive is enabled or its leaf parameters are configured with a resolver, an unauthenticated attacker can send crafted requests to cause a use-after-free issue in the worker process, resulting in a limited modification of memory data or a denial of service by forcing the process to restart.

To exploit this flaw, the ssl_verify_client directive must be set to "on" or "optional" and the ssl_ocsp directive must be enabled or its leaf parameters configured with a resolver, limiting its exposure as this is not the default configuration. This issue allows an attacker to have limited control to modify memory data from the worker process or cause a denial of service by forcing the process to restart, but it cannot cause a complete system denial of service. Due to these reasons, this flaw has been rated with a moderate severity.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, specifically set the OCSP responder using the ssl_ocsp_responder directive or switch from live OCSP validation to static CRL files using the ssl_crl directive. If neither configuration is possible, using a local DNS server to cache and quickly resolve OCSP responder names can reduce the probability of exploitation.