CVE-2022-21656: X.509 subjectAltName matching bypass in Envoy

Severity: medium (CVSS 5.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% 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. The default_validator.cc implementation used to implement the default certificate validation routines has a "type confusion" bug when processing subjectAltNames. This processing allows, for example, an rfc822Name or uniformResourceIndicator to be authenticated as a domain name. This confusion allows for the bypassing of nameConstraints, as processed by the underlying OpenSSL/BoringSSL implementation, exposing the possibility of impersonation of arbitrary servers. As a result Envoy will trust upstream certificates that should not be trusted.

Affected products

envoyproxy envoy: before 1.20.2 — fixed in 1.20.2

How to fix

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

References

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