Critical Yii2 Framework Vulnerability (CVE-2025-2690): Remote Code Execution Risk

A critical deserialization vulnerability (CVE-2025-2690) has been discovered in the Yii2 PHP framework, allowing remote code execution. This security flaw affects versions up to 2.0.39 and carries a CVSS score of 9.8 (Critical). Organizations using Yii2 should prioritize patching this vulnerability.

Executive Summary for Security Leadership

Key Points:

Vulnerability: Remote code execution via insecure deserialization in Yii2’s PHPUnit mock generation
Affected Versions: Yii2 ≤ 2.0.39
CVSS Score: 9.8 (Critical)
Attack Vector: Remote, unauthenticated
Public Exploits: Available in wild
Primary Risk: Complete system compromise
Mitigation: Immediate upgrade recommended

Technical Analysis

The vulnerability resides in the Generate function of phpunit\src\Framework\MockObject\MockClass.php, where improper deserialization of untrusted data occurs. This flaw enables attackers to craft malicious serialized objects that execute arbitrary code when deserialized by the application.

// Vulnerable code path in MockClass.php
public function Generate() {
    // ...
    $code = unserialize($serializedMock); // Insecure deserialization
    // ...
}

Security researchers have confirmed the vulnerability affects all Yii2 implementations using PHPUnit for testing, which includes many production environments where test components were inadvertently left enabled.

Impact Assessment

Successful exploitation could lead to:

Remote code execution with web server privileges
Complete application compromise
Lateral movement within affected networks
Data exfiltration
Server-side request forgery (SSRF) opportunities

Detection and Mitigation

Detection Methods:

Version check for Yii2 ≤ 2.0.39
Search for active exploitation attempts by monitoring for:
- Unusual PHPUnit-related requests
- Base64-encoded serialized objects in HTTP parameters
- Unexpected process spawning from web server contexts

# Sample log monitoring command for exploitation attempts
grep -E "(MockClass\.php|unserialize|phpunit)" /var/log/apache2/access.log

Mitigation Steps:

Immediate upgrade to Yii2 2.0.40 or later
Disable PHPUnit components in production environments
Implement input validation for all serialized data
Apply PHP’s unserialize_callback_func directive to restrict deserialization
Consider using the allowed_classes option with unserialize()

Operational Relevance

For Security Teams:

Prioritize patching any internet-facing Yii2 applications
Monitor for suspicious PHP process activity
Review SIEM rules for deserialization attack patterns

For Developers:

Review custom code for similar deserialization patterns
Remove test components from production builds
Implement secure alternatives like JSON for data serialization

Conclusion

CVE-2025-2690 represents a severe threat to organizations using vulnerable versions of the Yii2 framework. The combination of its critical severity, public exploit availability, and the framework’s widespread adoption demands immediate attention from security teams.