lib-oauth2: Fix possible timing attack in oauth2_validate_hmac()

Use mem_equals_timing_safe() instead of memcmp() to test the equality of the digest.

diff --git a/src/lib-oauth2/oauth2-jwt.c b/src/lib-oauth2/oauth2-jwt.c
index 527a0f3194165cedb6b76706fb65624f28101787..29c6fa55230b2811418707098806c103c821a171 100644 (file)
--- a/src/lib-oauth2/oauth2-jwt.c
+++ b/src/lib-oauth2/oauth2-jwt.c
@@ -105,7 +105,7 @@ static int oauth2_validate_hmac(const struct oauth2_settings *set,
        buffer_t *their_digest =
                t_base64url_decode_str(BASE64_DECODE_FLAG_NO_PADDING, blobs[2]);
        if (method->digest_size != their_digest->used ||
-           memcmp(digest, their_digest->data, method->digest_size) != 0) {
+           !mem_equals_timing_safe(digest, their_digest->data, method->digest_size)) {
                *error_r = "Incorrect JWT signature";
                return -1;
        }