CVE-2022-21657: X.509 Extended Key Usage and Trust Purposes bypass in Envoy

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2022-02-22 · updated 2026-06-17
Weakness: CWE-295

Description

Envoy is an open source edge and service proxy, designed for cloud-native applications. In affected versions Envoy does not restrict the set of certificates it accepts from the peer, either as a TLS client or a TLS server, to only those certificates that contain the necessary extendedKeyUsage (id-kp-serverAuth and id-kp-clientAuth, respectively). This means that a peer may present an e-mail certificate (e.g. id-kp-emailProtection), either as a leaf certificate or as a CA in the chain, and it will be accepted for TLS. This is particularly bad when combined with the issue described in pull request #630, in that it allows a Web PKI CA that is intended only for use with S/MIME, and thus exempted from audit or supervision, to issue TLS certificates that will be accepted by Envoy. As a result Envoy will trust upstream certificates that should not be trusted. There are no known workarounds to this issue. Users are advised to upgrade.

Affected products

envoyproxy envoy: before 1.18.6; from 1.19.0 before 1.19.3; from 1.20.0 before 1.20.2 — fixed in 1.18.6, 1.19.3, 1.20.2

How to fix

Upgrade to a fixed version: envoyproxy envoy 1.18.6, 1.19.3, 1.20.2. Check the vendor advisory for mitigations.

References

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