Cipher suite oddity

[Brian Candler]

Something just pointed out to me(*) that I don't understand:

TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA is in tls.CipherSuites()

TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 is in tls.InsecureCipherSuites()

Why is the SHA256 variant considered "insecure", but the SHA (presumably SHA1) variant "secure"?

Are these actually different cipher suites but with confusingly similar names?

(*) https://groups.google.com/g/prometheus-users/c/SJYu7cH_XKQ

[Brian Candler]

https://ciphersuite.info/cs/TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA/ (hex code 0xC0, 0x13)

https://ciphersuite.info/cs/TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256/ (hex code 0xC0, 0x27)
describes both as "weak", and at first glance there are fewer issues with the SHA256 variant as the hash is fixed.

But there's a comment in the (private) cipherSuitesPreferenceOrder in src/crypto/tls/cipher_suites.go:

//   - Anything else comes before CBC_SHA256
//
//     SHA-256 variants of the CBC ciphersuites don't implement any Lucky13
//     countermeasures. See http://www.isg.rhul.ac.uk/tls/Lucky13.html and

//     https://www.imperialviolet.org/2013/02/04/luckythirteen.html.

(the first link is broken BTW).  So I guess this could be why TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 didn't make the cut into "CipherSuites", whilst TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA did?