CVE-2026-21952: 
MySQL vulnerability analysis and mitigation

CVE-2026-21952 is a Denial of Service vulnerability in the MySQL Server Parser component, affecting Oracle MySQL Server versions 9.0.0 through 9.5.0. It was disclosed on January 20, 2026, as part of Oracle's January 2026 Critical Patch Update. The vulnerability allows a high-privileged attacker with network access to cause a hang or frequently repeatable crash of the MySQL Server. It carries a CVSS v3.1 base score of 4.9 (Medium) (Oracle Advisory).

The vulnerability is classified as CWE-400 (Uncontrolled Resource Consumption), residing in the MySQL Server's Parser component. A high-privileged attacker can send specially crafted input over multiple network protocols to trigger uncontrolled resource consumption, resulting in a server hang or crash. No user interaction is required, and the attack complexity is low, though exploitation requires high privileges (e.g., a valid database account with sufficient permissions). The CAPEC patterns associated with this vulnerability include Regular Expression Exponential Blowup (CAPEC-492) and XML Ping of the Death (CAPEC-147), suggesting the parser may be susceptible to pathological input patterns (Oracle Advisory).

Successful exploitation results in a complete Denial of Service — specifically, an unauthorized ability to cause a hang or frequently repeatable crash of the MySQL Server. The impact is limited to availability; there is no confidentiality or integrity impact. Because the vulnerability affects the database server process itself, exploitation could disrupt all applications and services dependent on the affected MySQL instance (Oracle Advisory).

Oracle has released patches for this vulnerability as part of the January 2026 Critical Patch Update (CPU), published January 20, 2026. Affected users should upgrade MySQL Server from versions 9.0.0–9.5.0 to a patched release provided in the CPU. As a temporary workaround, Oracle recommends restricting network access to the MySQL Server to only authorized administrators and implementing network segmentation to limit exposure. Oracle strongly advises against relying on workarounds as a long-term solution (Oracle Advisory).