CVE-2021-3007: Laminas-http RCE Vulnerability

CVE-2021-3007 Overview

CVE-2021-3007 is a critical insecure deserialization vulnerability affecting Laminas Project laminas-http before version 2.14.2 and Zend Framework 3.0.0. The vulnerability exists in the __destruct method of the Zend\Http\Response\Stream class within Stream.php. When attacker-controlled content can be deserialized, this flaw can be exploited to achieve remote code execution (RCE). Notably, Zend Framework is no longer supported by the maintainer, and while the laminas-http vendor considers this a "vulnerability in the PHP language itself," type checking mitigations have been implemented to prevent exploitation in unrecommended use cases where attacker-supplied data can be deserialized.

Critical Impact

This deserialization vulnerability enables remote code execution when attackers can control deserialized content, potentially leading to complete system compromise. The vulnerability has been observed being leveraged in botnet campaigns.

Affected Products

• Getlaminas laminas-http versions prior to 2.14.2
• Zend Framework version 3.0.0

Discovery Timeline

• 2021-01-04 - CVE-2021-3007 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-3007

Vulnerability Analysis

This insecure deserialization vulnerability exists in the Zend\Http\Response\Stream class, specifically within its __destruct magic method. PHP's deserialization mechanism automatically invokes magic methods such as __destruct when objects are unserialized. In vulnerable versions, the __destruct method in Stream.php performs file operations based on object properties that can be manipulated through crafted serialized data.

When an application deserializes user-controlled input containing a malicious Zend\Http\Response\Stream object, the attacker can control properties that determine file system operations. This can be chained with other techniques to achieve arbitrary code execution on the target system. The vulnerability follows a classic PHP object injection pattern where magic methods become gadgets in an exploitation chain.

According to Check Point research, this vulnerability has been actively leveraged in botnet campaigns, demonstrating real-world exploitation.

Root Cause

The root cause lies in the unsafe handling of object properties within the __destruct method of the Stream class. When a serialized object is deserialized, the destructor executes operations that trust object property values without proper type validation. This allows an attacker to inject malicious property values that, when processed during object destruction, lead to unintended code execution or file system manipulation. The fix implemented in version 2.14.2 adds type checking to validate property values before they are used in sensitive operations.

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction. An attacker must identify an application endpoint that deserializes user-supplied input and processes it using the vulnerable laminas-http or Zend Framework components. The exploitation flow involves:

1. Crafting a malicious serialized PHP object containing a Zend\Http\Response\Stream instance with manipulated properties
2. Submitting the payload to an application endpoint that performs deserialization
3. The PHP runtime automatically invokes the __destruct method when the object is destroyed
4. Malicious property values trigger unintended operations leading to code execution

The vulnerability mechanism involves object property manipulation during deserialization. When the destructor runs, it processes the streamName property in file operations. Technical details and exploitation techniques are documented in the GitHub RCE Exploit Document. The fix involves adding strict type checking to prevent arbitrary values from being processed.

Detection Methods for CVE-2021-3007

Indicators of Compromise

• Unexpected serialized PHP data containing Zend\Http\Response\Stream class references in HTTP requests
• Suspicious file operations or new files created in web-accessible directories
• Unusual network traffic patterns indicating botnet command and control communications
• Web application logs showing malformed or unusually large serialized payloads

Detection Strategies

• Monitor web application logs for requests containing serialized PHP objects (base64-encoded O: patterns)
• Deploy web application firewall rules to detect and block PHP serialized object payloads
• Implement file integrity monitoring on application directories to detect unauthorized file creation
• Review application code for unserialize() calls processing user-controlled input

Monitoring Recommendations

• Enable verbose logging for PHP applications to capture deserialization events
• Configure SIEM rules to alert on suspicious patterns matching PHP object injection attempts
• Monitor for outbound connections to known botnet infrastructure associated with CVE-2021-3007 exploitation
• Regularly scan application dependencies to identify vulnerable laminas-http or Zend Framework versions

How to Mitigate CVE-2021-3007

Immediate Actions Required

• Upgrade laminas-http to version 2.14.2 or later immediately
• Audit applications using Zend Framework 3.0.0 for deserialization of user input
• Migrate away from Zend Framework to actively maintained alternatives as it is no longer supported
• Implement input validation to reject serialized PHP objects from untrusted sources

Patch Information

The vulnerability has been addressed in laminas-http version 2.14.2, which implements type checking to prevent exploitation. Review the Laminas HTTP Release Notes for details on the security fix. The patch adds validation to ensure property values are of expected types before they are used in sensitive operations. For technical details on the changes, refer to the Laminas HTTP Pull Request and commit history.

Workarounds

• Avoid deserializing user-controlled data entirely; use JSON or other safe formats instead
• If deserialization is required, implement allow-lists of permitted classes using PHP's allowed_classes option
• Deploy web application firewalls to filter requests containing serialized PHP objects
• Isolate applications using vulnerable components in network segments with restricted outbound access

# Update laminas-http using Composer
composer require laminas/laminas-http:^2.14.2

# Verify installed version
composer show laminas/laminas-http | grep versions

# Search for unserialize usage in codebase
grep -r "unserialize" --include="*.php" /path/to/application