CVE-2021-35583: Oracle MySQL Server DOS Vulnerability

CVE-2021-35583 Overview

CVE-2021-35583 is a Denial of Service vulnerability affecting the MySQL Server product of Oracle MySQL, specifically within the Server: Windows component. This easily exploitable vulnerability allows an unauthenticated attacker with network access via multiple protocols to compromise MySQL Server availability. Successful exploitation can result in an unauthorized ability to cause a hang or frequently repeatable crash, leading to a complete denial of service condition.

Critical Impact

Unauthenticated remote attackers can cause complete denial of service of MySQL Server instances on Windows systems through network-accessible protocols.

Affected Products

• Oracle MySQL Server versions 8.0.25 and prior
• NetApp OnCommand Insight
• NetApp SnapCenter

Discovery Timeline

• October 20, 2021 - CVE-2021-35583 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2021-35583

Vulnerability Analysis

This vulnerability exists within the Windows-specific component of Oracle MySQL Server. The flaw allows remote, unauthenticated attackers to trigger a denial of service condition without requiring any user interaction. The vulnerability is characterized by its ease of exploitation—attackers can leverage multiple network protocols to reach the vulnerable component, making it particularly dangerous in environments where MySQL servers are exposed to untrusted networks.

The impact is limited to availability; there is no impact to confidentiality or integrity of data stored within the MySQL database. However, the ability to repeatedly crash or hang the database server can have severe operational consequences for organizations relying on MySQL for critical business operations.

Root Cause

The root cause is related to improper handling within the Windows component of MySQL Server. While Oracle has not disclosed specific technical details about the underlying flaw (classified as NVD-CWE-noinfo), the vulnerability allows malicious input received over the network to trigger a crash or hang condition in the server process. This type of availability-focused vulnerability typically stems from unhandled exceptions, resource exhaustion, or improper state management when processing certain requests.

Attack Vector

The attack can be executed remotely over the network without authentication. The attacker does not need valid credentials or any prior access to the MySQL server. The vulnerability can be triggered through multiple network protocols supported by MySQL Server.

The attack flow involves:

1. The attacker identifies a MySQL Server instance running on Windows
2. The attacker sends specially crafted network requests to the server
3. The MySQL Server process enters a hang state or crashes
4. Service availability is disrupted until manual intervention or automatic restart occurs

Since the attack requires only network access and no authentication, any MySQL Server on Windows that is reachable from untrusted networks is potentially at risk.

Detection Methods for CVE-2021-35583

Indicators of Compromise

• Unexpected MySQL Server process crashes or restarts on Windows systems
• Service availability alerts indicating MySQL Server is unresponsive
• Unusual network traffic patterns targeting MySQL ports (typically 3306)
• Windows Event Log entries showing MySQL service termination

Detection Strategies

• Monitor MySQL Server process stability and implement alerting for unexpected crashes or restarts
• Analyze network traffic for anomalous connection patterns to MySQL Server ports
• Review MySQL error logs for crash dumps or hang indicators
• Implement network intrusion detection rules for suspicious MySQL protocol traffic
• Deploy endpoint detection solutions to monitor MySQL process behavior

Monitoring Recommendations

• Enable comprehensive MySQL Server error logging and monitor logs for crash indicators
• Configure Windows Event Log monitoring for MySQL service state changes
• Implement availability monitoring with short polling intervals to detect denial of service conditions quickly
• Set up network traffic baseline analysis to identify unusual connection volumes to MySQL ports

How to Mitigate CVE-2021-35583

Immediate Actions Required

• Update Oracle MySQL Server to a version newer than 8.0.25 as specified in the Oracle Critical Patch Update
• Restrict network access to MySQL Server to trusted networks and hosts only
• Implement firewall rules to limit exposure of MySQL ports to untrusted networks
• Review and harden MySQL Server configuration according to Oracle security best practices

Patch Information

Oracle has addressed this vulnerability in the October 2021 Critical Patch Update. Administrators should apply the patch available through the Oracle Critical Patch Update. For NetApp products that incorporate MySQL Server, refer to the NetApp Security Advisory for specific guidance on affected versions and remediation steps.

Workarounds

• Implement network segmentation to isolate MySQL Server instances from untrusted networks
• Configure firewall rules to allow MySQL connections only from known, trusted IP addresses
• Consider using a VPN or SSH tunneling for remote database access instead of direct exposure
• Implement connection rate limiting at the network level to reduce impact of potential DoS attacks

# Example: Restrict MySQL access using Windows Firewall
# Allow MySQL connections only from trusted subnet
netsh advfirewall firewall add rule name="MySQL Trusted Access" dir=in action=allow protocol=TCP localport=3306 remoteip=192.168.1.0/24

# Block all other inbound MySQL connections
netsh advfirewall firewall add rule name="MySQL Block Untrusted" dir=in action=block protocol=TCP localport=3306