GHSA-gr79-9v6v-gc9r

Dex 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: TLS_RSA_WITH_AES_256_CBC_SHA 256 TLS_RSA_WITH_AES_128_CBC_SHA 128 TLS_RSA_WITH_3DES_EDE_CBC_SHA 168 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA 256 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA 128 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA 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: TLS_RSA_WITH_AES_256_CBC_SHA 256 TLS_RSA_WITH_AES_128_CBC_SHA 128 TLS_RSA_WITH_3DES_EDE_CBC_SHA 168 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA 256 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA 128 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA 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: TLS_RSA_WITH_AES_256_GCM_SHA384 256 TLS_RSA_WITH_AES_256_CBC_SHA 256 TLS_RSA_WITH_AES_128_GCM_SHA256 128 TLS_RSA_WITH_AES_128_CBC_SHA 128 TLS_RSA_WITH_3DES_EDE_CBC_SHA 168 TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 256 ECDH: X25519 (253 bits) TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 256 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA 256 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 128 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA 128 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA 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: TLS_CHACHA20_POLY1305_SHA256 256 ECDH: X25519 (253 bits) TLS_AES_256_GCM_SHA384 256 ECDH: X25519 (253 bits) TLS_AES_128_GCM_SHA256 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: TLS_RSA_WITH_AES_256_GCM_SHA384 256 TLS_RSA_WITH_AES_128_GCM_SHA256 128 TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 256 ECDH: X25519 (253 bits) TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 256 ECDH: prime256v1 (256 bits) TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 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: TLS_CHACHA20_POLY1305_SHA256 256 ECDH: X25519 (253 bits) TLS_AES_256_GCM_SHA384 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.