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CVE-2021-35610

7.1 HIGH
Denial of Service

📋 TL;DR

This vulnerability in MySQL Server's optimizer component allows authenticated attackers with network access to cause denial of service (server hangs or crashes) and perform unauthorized data modifications. It affects MySQL Server versions 8.0.26 and earlier, requiring only low-privileged database access.

💻 Affected Systems

Products:
  • Oracle MySQL Server
Versions: 8.0.26 and prior
Operating Systems: All platforms running affected MySQL versions
Default Config Vulnerable: ⚠️ Yes
Notes: Affects the optimizer component; requires attacker to have CREATE/INSERT/DELETE privileges or similar low-level database access.

📦 What is this software?

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⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete database server outage (DoS) combined with unauthorized data manipulation affecting critical business operations.

🟠

Likely Case

Service disruption through repeated crashes and potential data integrity issues from unauthorized modifications.

🟢

If Mitigated

Limited impact if proper network segmentation and privilege controls prevent low-privileged users from exploiting the vulnerability.

🌐 Internet-Facing: HIGH - Network accessible with low attack complexity and authentication requirements.
🏢 Internal Only: MEDIUM - Requires authenticated access but low privilege requirements make internal exploitation feasible.

🎯 Exploit Status

Public PoC: ✅ No
Weaponized: UNKNOWN
Unauthenticated Exploit: ✅ No
Complexity: LOW

Oracle rates as 'easily exploitable' but requires authenticated access; specific exploit details not publicly documented.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 8.0.27 and later

Vendor Advisory: https://www.oracle.com/security-alerts/cpuoct2021.html

Restart Required: Yes

Instructions:

1. Download MySQL 8.0.27 or later from Oracle. 2. Backup databases. 3. Stop MySQL service. 4. Install updated version. 5. Restart MySQL service. 6. Verify version with 'SELECT VERSION();'

🔧 Temporary Workarounds

Restrict Database Privileges

all

Minimize attack surface by limiting CREATE, INSERT, DELETE, and UPDATE privileges to essential users only.

REVOKE CREATE, INSERT, DELETE, UPDATE ON *.* FROM 'lowprivuser'@'%';
FLUSH PRIVILEGES;

Network Access Controls

linux

Restrict MySQL network access to trusted IP addresses only.

# In my.cnf: bind-address = trusted_ip
# Firewall rule: iptables -A INPUT -p tcp --dport 3306 -s trusted_ip -j ACCEPT

🧯 If You Can't Patch

  • Implement strict network segmentation to isolate MySQL servers from untrusted networks
  • Apply principle of least privilege to all database users and regularly audit permissions

🔍 How to Verify

Check if Vulnerable:

Connect to MySQL and run: SELECT VERSION(); If version is 8.0.26 or earlier, system is vulnerable.

Check Version:

mysql -u username -p -e 'SELECT VERSION();'

Verify Fix Applied:

After patching, run: SELECT VERSION(); Should show 8.0.27 or later. Test optimizer functionality with complex queries.

📡 Detection & Monitoring

Log Indicators:

  • Multiple optimizer-related errors in MySQL error log
  • Unexpected server crashes or hangs
  • Unusual CREATE/INSERT/DELETE operations from low-privileged users

Network Indicators:

  • Multiple failed optimizer-related queries from single source
  • Abnormal query patterns targeting optimizer functions

SIEM Query:

source="mysql.log" ("optimizer" AND (error OR crash)) OR ("Access denied" AND "CREATE|INSERT|DELETE")

📊 Metadata

CVE ID: CVE-2021-35610
CVSS v3 Score: 7.1 (HIGH)
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H
Published: October 20, 2021
Last Updated: November 21, 2024

🔗 References

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