Envoy Proxy Incorrect Authorization Vulnerability - CVE-2021-32779

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions envoy incorrectly handled a URI 39fragment39 element as part of the path element. Envoy is configured with an RBAC filter for authorization or similar mechanism with an explicit case of a final quot/adminquot path element or is using a negative assertion with final path element of quot/adminquot. The client sends request to quot/app1/adminfooquot. In Envoy prior to 1.18.0 or 1.18.0 configured with path_normalizationfalse. Envoy treats fragment as a suffix of the query string when present or as a suffix of the path when query string is absent so it evaluates the final path element as quot/adminfooquot and mismatches with the configured quot/adminquot path element. In Envoy 1.18.0 configured with path_normalizationtrue. Envoy transforms this to /app1/admin23foo and mismatches with the configured /admin prefix. The resulting URI is sent to the next server-agent with the offending quotfooquot fragment which violates RFC3986 or with the nonsensical quot23fooquot text appended. A specifically constructed request with URI containing 39fragment39 element delivered by an untrusted client in the presence of path based request authorization resulting in escalation of Privileges when path based request authorization extensions. Envoy versions 1.19.1 1.18.4 1.17.4 1.16.5 contain fixes that removes fragment from URI path in incoming requests.