CVE-2026-47775: Envoy OAuth2 Filter: Padding Oracle via AES-256-CBC Cookie Decryption
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 filter's 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 codeverifier in ~6,200 requests (~100 seconds), then exchange it with a stolen authorization code to obtain the victim's access token. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Envoy OAuth2 HTTP filter (encrypt()/decrypt() for CodeVerifier cookie)to a version that resolves this vulnerability.Fixed in 1.35.11 - Upgrade
Upgrade
Envoy OAuth2 HTTP filter (encrypt()/decrypt() for CodeVerifier cookie)to a version that resolves this vulnerability.Fixed in 1.36.7 - Upgrade
Upgrade
Envoy OAuth2 HTTP filter (encrypt()/decrypt() for CodeVerifier cookie)to a version that resolves this vulnerability.Fixed in 1.37.3 - Upgrade
Upgrade
Envoy OAuth2 HTTP filter (encrypt()/decrypt() for CodeVerifier cookie)to a version that resolves this vulnerability.Fixed in 1.38.1
Event History
Frequently Asked Questions
What is the severity of CVE-2026-47775?
CVE-2026-47775 has a medium severity rating of 6.8.
How do I fix CVE-2026-47775?
To fix CVE-2026-47775, update Envoy to versions 1.35.11, 1.36.7, 1.37.3, or 1.38.1 or later.
What type of vulnerability is CVE-2026-47775?
CVE-2026-47775 is a padding oracle vulnerability due to improper use of AES-256-CBC for cookie decryption.
Which software is affected by CVE-2026-47775?
CVE-2026-47775 affects the Envoy OAuth2 HTTP filter.
What potential impact does CVE-2026-47775 have?
CVE-2026-47775 can lead to the exposure of sensitive data due to improper encryption mechanisms.