mod_auth_openidc is an OpenID Certified authentication and authorization module for the Apache 2.x HTTP server that implements the OpenID Connect Relying Party functionality. Prior to 2.4.19.4, an out-of-bounds read and a one-byte out-of-bounds write exist in the state-cookie parser of `mod_auth_openidc`. The issue is fixed in version 2.4.19.4 by stopping the scan at the string terminator so a value-less token is rejected. No in-product workarounds are available. As a stop-gap, an upstream reverse proxy or WAF that rejects or normalizes malformed `Cookie` headers (tokens lacking `=`) can reduce exposure, but upgrading is the recommended remediation.

CVE-2026-54789 affects mod_auth_openidc, an OpenID Certified authentication and authorization module for Apache 2.x HTTP servers. The vulnerability exists in the state-cookie parser, where an out-of-bounds read and a one-byte out-of-bounds write can be triggered by malformed Cookie headers containing tokens that lack an '=' character. The flaw impacts all versions prior to 2.4.19.4. The fix was introduced in version 2.4.19.4 by enforcing a scan stop at the string terminator, causing value-less tokens to be rejected. No in-product workarounds are available, making upgrading the primary recommended remediation. As a temporary mitigation, deploying an upstream reverse proxy or WAF that rejects or normalizes malformed Cookie headers can reduce exposure. The vulnerability poses a risk to systems relying on OpenID Connect authentication via Apache modules.