From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 11 May 2026 12:13:49 +0000 (-0700)
Subject: Apply timingsafe_bcmp() in authentication paths
X-Git-Tag: REL_16_14~14
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=00e27235e5ef6596acc94ec60eb17f74810bf817;p=thirdparty%2Fpostgresql.git

Apply timingsafe_bcmp() in authentication paths

This commit applies timingsafe_bcmp() to authentication paths that
handle attributes or data previously compared with memcpy() or strcmp(),
which are sensitive to timing attacks.

The following data is concerned by this change, some being in the
backend and some in the frontend:
- For a SCRAM or MD5 password, the computed key or the MD5 hash compared
with a password during a plain authentication.
- For a SCRAM exchange, the stored key, the client's final nonce and the
server nonce.
- RADIUS (up to v18), the encrypted password.
- For MD5 authentication, the MD5(MD5()) hash.

Reported-by: Joe Conway <mail@joeconway.com>
Security: CVE-2026-6478
Author: Michael Paquier <michael@paquier.xyz>
Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Backpatch-through: 14
---

diff --git a/src/backend/libpq/auth-scram.c b/src/backend/libpq/auth-scram.c
index 9b286aa4d7f..1b9e1cc0cc1 100644
--- a/src/backend/libpq/auth-scram.c
+++ b/src/backend/libpq/auth-scram.c
@@ -577,7 +577,7 @@ scram_verify_plain_password(const char *username, const char *password,
 	 * Compare the secret's Server Key with the one computed from the
 	 * user-supplied password.
 	 */
-	return memcmp(computed_key, server_key, key_length) == 0;
+	return timingsafe_bcmp(computed_key, server_key, key_length) == 0;
 }
 
 
@@ -1125,9 +1125,9 @@ verify_final_nonce(scram_state *state)
 
 	if (final_nonce_len != client_nonce_len + server_nonce_len)
 		return false;
-	if (memcmp(state->client_final_nonce, state->client_nonce, client_nonce_len) != 0)
+	if (timingsafe_bcmp(state->client_final_nonce, state->client_nonce, client_nonce_len) != 0)
 		return false;
-	if (memcmp(state->client_final_nonce + client_nonce_len, state->server_nonce, server_nonce_len) != 0)
+	if (timingsafe_bcmp(state->client_final_nonce + client_nonce_len, state->server_nonce, server_nonce_len) != 0)
 		return false;
 
 	return true;
@@ -1182,7 +1182,7 @@ verify_client_proof(scram_state *state)
 				client_StoredKey, &errstr) < 0)
 		elog(ERROR, "could not hash stored key: %s", errstr);
 
-	if (memcmp(client_StoredKey, state->StoredKey, state->key_length) != 0)
+	if (timingsafe_bcmp(client_StoredKey, state->StoredKey, state->key_length) != 0)
 		return false;
 
 	return true;
diff --git a/src/backend/libpq/auth.c b/src/backend/libpq/auth.c
index 183d9e731d6..ea149e478b0 100644
--- a/src/backend/libpq/auth.c
+++ b/src/backend/libpq/auth.c
@@ -3248,7 +3248,7 @@ PerformRadiusTransaction(const char *server, const char *secret, const char *por
 		}
 		pfree(cryptvector);
 
-		if (memcmp(receivepacket->vector, encryptedpassword, RADIUS_VECTOR_LENGTH) != 0)
+		if (timingsafe_bcmp(receivepacket->vector, encryptedpassword, RADIUS_VECTOR_LENGTH) != 0)
 		{
 			ereport(LOG,
 					(errmsg("RADIUS response from %s has incorrect MD5 signature",
diff --git a/src/backend/libpq/crypt.c b/src/backend/libpq/crypt.c
index ef496a0bea9..3e67e75fe84 100644
--- a/src/backend/libpq/crypt.c
+++ b/src/backend/libpq/crypt.c
@@ -197,7 +197,8 @@ md5_crypt_verify(const char *role, const char *shadow_pass,
 		return STATUS_ERROR;
 	}
 
-	if (strcmp(client_pass, crypt_pwd) == 0)
+	if (strlen(client_pass) == strlen(crypt_pwd) &&
+		timingsafe_bcmp(client_pass, crypt_pwd, strlen(crypt_pwd)) == 0)
 		retval = STATUS_OK;
 	else
 	{
@@ -259,7 +260,8 @@ plain_crypt_verify(const char *role, const char *shadow_pass,
 				*logdetail = errstr;
 				return STATUS_ERROR;
 			}
-			if (strcmp(crypt_client_pass, shadow_pass) == 0)
+			if (strlen(crypt_client_pass) == strlen(shadow_pass) &&
+				timingsafe_bcmp(crypt_client_pass, shadow_pass, strlen(shadow_pass)) == 0)
 				return STATUS_OK;
 			else
 			{
diff --git a/src/interfaces/libpq/fe-auth-scram.c b/src/interfaces/libpq/fe-auth-scram.c
index 6b779ec7ffd..4219e21b3fb 100644
--- a/src/interfaces/libpq/fe-auth-scram.c
+++ b/src/interfaces/libpq/fe-auth-scram.c
@@ -632,7 +632,7 @@ read_server_first_message(fe_scram_state *state, char *input)
 
 	/* Verify immediately that the server used our part of the nonce */
 	if (strlen(nonce) < strlen(state->client_nonce) ||
-		memcmp(nonce, state->client_nonce, strlen(state->client_nonce)) != 0)
+		timingsafe_bcmp(nonce, state->client_nonce, strlen(state->client_nonce)) != 0)
 	{
 		libpq_append_conn_error(conn, "invalid SCRAM response (nonce mismatch)");
 		return false;
@@ -879,8 +879,8 @@ verify_server_signature(fe_scram_state *state, bool *match,
 	pg_hmac_free(ctx);
 
 	/* signature processed, so now check after it */
-	if (memcmp(expected_ServerSignature, state->ServerSignature,
-			   state->key_length) != 0)
+	if (timingsafe_bcmp(expected_ServerSignature, state->ServerSignature,
+						state->key_length) != 0)
 		*match = false;
 	else
 		*match = true;