Envoy Proxy Generation of Error Message Containing Sensitive Information Vulnerability - CVE-2026-47775

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11 1.36.7 1.37.3 and 1.38.1 the OAuth2 HTTP filter39s encrypt()/decrypt() functions use AES-256-CBC without an authentication tag (no HMAC no AEAD). The /callback endpoint returns HTTP 302 on successful decryption and HTTP 401 on padding failure creating a padding oracle. An attacker who obtains the encrypted CodeVerifier cookie can recover the plaintext PKCE code_verifier in 6200 requests (100 seconds) then exchange it with a stolen authorization code to obtain the victim39s access token. This vulnerability is fixed in 1.35.11 1.36.7 1.37.3 and 1.38.1.