CVE-2022-21657: 
NixOS vulnerability analysis and mitigation

A vulnerability was discovered in Envoy (CVE-2022-21657) where it does not properly restrict the set of certificates it accepts from peers during TLS connections. The issue affects Envoy versions 1.20.1 and earlier, with patches available in versions 1.18.6, 1.19.3, and 1.20.2 (Envoy Advisory).

The vulnerability stems from Envoy's failure to validate the Extended Key Usage (EKU) and Trust Purposes in X.509 certificates. Specifically, it does not restrict certificates to those containing the necessary extendedKeyUsage (id-kp-serverAuth for servers and id-kp-clientAuth for clients). This allows peers to present certificates intended for other purposes, such as email certificates (id-kp-emailProtection), either as leaf certificates or as CAs in the chain (Envoy Advisory). The vulnerability has been assigned a CVSS v3.1 score of 3.1 (Low) with vector AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N.

The primary impact is that Envoy will accept and trust upstream certificates that should not be trusted. This is particularly concerning when combined with other issues, as it could allow a Web PKI CA intended only for S/MIME usage, and thus exempt from certain audit or supervision requirements, to issue TLS certificates that Envoy would accept (Envoy Advisory).

The vulnerability has been patched in Envoy versions 1.18.6, 1.19.3, and 1.20.2. No workarounds are available, making upgrading to a patched version the only mitigation option (Envoy Advisory).