CVE-2024-23656: Dex 2.37.0 is discarding TLSconfig and always serves deprecated TLS 1.0/1.1 and insecure ciphers

Summary

Dex 2.37.0 is serving HTTPS with insecure TLS 1.0 and TLS 1.1.

Details While working on https://github.com/dexidp/dex/issues/2848 and implementing configurable TLS support, I noticed my changes did not have any effect in TLS config, so I started investigating.

https://github.com/dexidp/dex/blob/70d7a2c7c1bb2646b1a540e49616cbc39622fb83/cmd/dex/serve.go#L425 is seemingly setting TLS 1.2 as minimum version, but the whole tlsConfig is ignored after "TLS cert reloader" was introduced in https://github.com/dexidp/dex/pull/2964. Configured cipher suites are not respected either, as seen on the output.

PoC Build Dex, generate certs with gencert.sh, modify config.dev.yaml to run on https, using generated certs.

console issuer: http://127.0.0.1:5556/dex

storage: type: sqlite3 config: file: dex.db

web: https: 127.0.0.1:5556 tlsCert: examples/k8s/ssl/cert.pem tlsKey: examples/k8s/ssl/key.pem

<rest as default>

Run dex bin/dex serve config.dev.yaml.

Install sslyze, easy to use SSL connection analyzer:

console pip3 install sslyze sslyze 127.0.0.1:5556

In Dex 2.37.0, TLS 1.0 and TLS 1.1 are enabled in addition to expected TLS 1.2 and TLS 1.3. console TLS 1.0 Cipher Suites: Attempted to connect using 80 cipher suites.

The server accepted the following 6 cipher suites: TLSRSAWITHAES256CBCSHA 256 TLSRSAWITHAES128CBCSHA 128 TLSRSAWITH3DESEDECBCSHA 168 TLSECDHERSAWITHAES256CBCSHA 256 ECDH: prime256v1 (256 bits) TLSECDHERSAWITHAES128CBCSHA 128 ECDH: prime256v1 (256 bits) TLSECDHERSAWITH3DESEDECBCSHA 168 ECDH: prime256v1 (256 bits)

The group of cipher suites supported by the server has the following properties: Forward Secrecy OK - Supported Legacy RC4 Algorithm OK - Not Supported

TLS 1.1 Cipher Suites: Attempted to connect using 80 cipher suites.

The server accepted the following 6 cipher suites: TLSRSAWITHAES256CBCSHA 256 TLSRSAWITHAES128CBCSHA 128 TLSRSAWITH3DESEDECBCSHA 168 TLSECDHERSAWITHAES256CBCSHA 256 ECDH: prime256v1 (256 bits) TLSECDHERSAWITHAES128CBCSHA 128 ECDH: prime256v1 (256 bits) TLSECDHERSAWITH3DESEDECBCSHA 168 ECDH: prime256v1 (256 bits)

The group of cipher suites supported by the server has the following properties: Forward Secrecy OK - Supported Legacy RC4 Algorithm OK - Not Supported

TLS 1.2 Cipher Suites: Attempted to connect using 156 cipher suites.

The server accepted the following 11 cipher suites: TLSRSAWITHAES256GCMSHA384 256 TLSRSAWITHAES256CBCSHA 256 TLSRSAWITHAES128GCMSHA256 128 TLSRSAWITHAES128CBCSHA 128 TLSRSAWITH3DESEDECBCSHA 168 TLSECDHERSAWITHCHACHA20POLY1305SHA256 256 ECDH: X25519 (253 bits) TLSECDHERSAWITHAES256GCMSHA384 256 ECDH: prime256v1 (256 bits) TLSECDHERSAWITHAES256CBCSHA 256 ECDH: prime256v1 (256 bits) TLSECDHERSAWITHAES128GCMSHA256 128 ECDH: prime256v1 (256 bits) TLSECDHERSAWITHAES128CBCSHA 128 ECDH: prime256v1 (256 bits) TLSECDHERSAWITH3DESEDECBCSHA 168 ECDH: prime256v1 (256 bits)

The group of cipher suites supported by the server has the following properties: Forward Secrecy OK - Supported Legacy RC4 Algorithm OK - Not Supported

TLS 1.3 Cipher Suites: Attempted to connect using 5 cipher suites.

The server accepted the following 3 cipher suites: TLSCHACHA20POLY1305SHA256 256 ECDH: X25519 (253 bits) TLSAES256GCMSHA384 256 ECDH: X25519 (253 bits) TLSAES128GCMSHA256 128 ECDH: X25519 (253 bits)

In Dex 2.36.0, TLS 1.0 and TLS 1.1 are disabled as expected. console TLS 1.0 Cipher Suites: Attempted to connect using 80 cipher suites; the server rejected all cipher suites.

TLS 1.1 Cipher Suites: Attempted to connect using 80 cipher suites; the server rejected all cipher suites.

TLS 1.2 Cipher Suites: Attempted to connect using 156 cipher suites.

The server accepted the following 5 cipher suites: TLSRSAWITHAES256GCMSHA384 256 TLSRSAWITHAES128GCMSHA256 128 TLSECDHERSAWITHCHACHA20POLY1305SHA256 256 ECDH: X25519 (253 bits) TLSECDHERSAWITHAES256GCMSHA384 256 ECDH: prime256v1 (256 bits) TLSECDHERSAWITHAES128GCMSHA256 128 ECDH: prime256v1 (256 bits)

The group of cipher suites supported by the server has the following properties: Forward Secrecy OK - Supported Legacy RC4 Algorithm OK - Not Supported

TLS 1.3 Cipher Suites: Attempted to connect using 5 cipher suites.

The server accepted the following 3 cipher suites: TLSCHACHA20POLY1305SHA256 256 ECDH: X25519 (253 bits) TLSAES256GCMSHA384 256 ECDH: X25519 (253 bits)

Impact TLS 1.0 and TLS 1.1 connections can be decrypted by the attacker, and hence decrypt the traffic to Dex.