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Code Issues 116 Packages Projects Releases 10 Wiki Activity

fix: use constant time comparisons when validating PKCE challenges (#1047)

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This commit is contained in:
Alessandro (Ale) Segala
2025-10-23 23:30:50 -07:00
committed by GitHub
parent 35d913f905
commit eb3963d0fc
2 changed files with 39 additions and 7 deletions
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19
backend/internal/service/oidc_service.go
View File

@@ -3,6 +3,7 @@ package service
import (
"context"
"crypto/sha256"
"crypto/subtle"
"crypto/tls"
"encoding/base64"
"encoding/json"
@@ -394,7 +395,7 @@ func (s *OidcService) createTokenFromAuthorizationCode(ctx context.Context, inpu
// If the client is public or PKCE is enabled, the code verifier must match the code challenge
if client.IsPublic || client.PkceEnabled {
if !s.validateCodeVerifier(input.CodeVerifier, *authorizationCodeMetaData.CodeChallenge, *authorizationCodeMetaData.CodeChallengeMethodSha256) {
if !validateCodeVerifier(input.CodeVerifier, *authorizationCodeMetaData.CodeChallenge, *authorizationCodeMetaData.CodeChallengeMethodSha256) {
return CreatedTokens{}, &common.OidcInvalidCodeVerifierError{}
}
}
@@ -1083,13 +1084,20 @@ func (s *OidcService) createAuthorizationCode(ctx context.Context, clientID stri
return randomString, nil
}
func (s *OidcService) validateCodeVerifier(codeVerifier, codeChallenge string, codeChallengeMethodSha256 bool) bool {
func validateCodeVerifier(codeVerifier, codeChallenge string, codeChallengeMethodSha256 bool) bool {
if codeVerifier == "" || codeChallenge == "" {
return false
}
if !codeChallengeMethodSha256 {
return codeVerifier == codeChallenge
return subtle.ConstantTimeCompare([]byte(codeVerifier), []byte(codeChallenge)) == 1
}
// Base64 URL decode the challenge
// If it's not valid base64url, fail the operation
codeChallengeBytes, err := base64.RawURLEncoding.DecodeString(codeChallenge)
if err != nil {
return false
}
// Compute SHA-256 hash of the codeVerifier
@@ -1097,10 +1105,7 @@ func (s *OidcService) validateCodeVerifier(codeVerifier, codeChallenge string, c
h.Write([]byte(codeVerifier))
codeVerifierHash := h.Sum(nil)
// Base64 URL encode the verifier hash
encodedVerifierHash := base64.RawURLEncoding.EncodeToString(codeVerifierHash)
return encodedVerifierHash == codeChallenge
return subtle.ConstantTimeCompare(codeVerifierHash, codeChallengeBytes) == 1
}
func (s *OidcService) getCallbackURL(client *model.OidcClient, inputCallbackURL string, tx *gorm.DB, ctx context.Context) (callbackURL string, err error) {

27
backend/internal/service/oidc_service_test.go
View File

@@ -5,6 +5,8 @@ import (
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/sha256"
"encoding/base64"
"encoding/json"
"net/http"
"testing"
@@ -510,3 +512,28 @@ func TestOidcService_verifyClientCredentialsInternal(t *testing.T) {
})
})
}
func TestValidateCodeVerifier_Plain(t *testing.T) {
require.False(t, validateCodeVerifier("", "", false))
require.False(t, validateCodeVerifier("", "", true))
t.Run("plain", func(t *testing.T) {
require.False(t, validateCodeVerifier("", "challenge", false))
require.False(t, validateCodeVerifier("verifier", "", false))
require.True(t, validateCodeVerifier("plainVerifier", "plainVerifier", false))
require.False(t, validateCodeVerifier("plainVerifier", "otherVerifier", false))
})
t.Run("SHA 256", func(t *testing.T) {
codeVerifier := "dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"
hash := sha256.Sum256([]byte(codeVerifier))
codeChallenge := base64.RawURLEncoding.EncodeToString(hash[:])
require.True(t, validateCodeVerifier(codeVerifier, codeChallenge, true))
require.False(t, validateCodeVerifier("wrongVerifier", codeChallenge, true))
require.False(t, validateCodeVerifier(codeVerifier, "!", true))
// Invalid base64
require.False(t, validateCodeVerifier("NOT!VALID", codeChallenge, true))
})
}