CVE-2026-47220 is a NULL pointer dereference vulnerability in Envoy proxy affecting versions 1.37.0 through 1.37.4 and version 1.38.3. The flaw triggers when the %REQUESTED_SERVER_NAME(X:Y)% log format specifier is used alongside host-related options such as HOST_FIRST or SNI_FIRST, and the incoming request lacks the host header. This leads to a crash of the Envoy process. The vulnerability is addressed in version 1.37.5 and later versions except 1.38.3, which remains affected. No known exploits are reported in the wild. The CVSS v3.1 base score is 7.5, indicating high severity with network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability (denial of service).

Successful exploitation causes a denial of service by crashing the Envoy proxy process when processing requests missing the host header under specific logging configurations. There is no confidentiality or integrity impact reported. The vulnerability can be triggered remotely without authentication or user interaction.

A fix is available in Envoy version 1.37.5, which resolves the NULL pointer dereference issue. Users should upgrade to version 1.37.5 or later versions that do not include the vulnerability. Version 1.38.3 remains affected and should not be used without mitigation. No vendor advisory explicitly states alternative mitigations or workarounds. Patch status is confirmed by the vendor advisory. Users should consult the Red Hat advisory for additional details and apply the official fix.