CVE-2024-55885

Executive Summary

CVE-2024-55885 identifies a critical cryptographic weakness in the Beego web framework for Go, where versions prior to 2.3.4 use the MD5 hashing algorithm. MD5 is cryptographically broken and susceptible to collision attacks, allowing an attacker to generate two different inputs that produce the same hash. This vulnerability can be exploited to bypass authentication, forge session tokens, or manipulate data integrity checks. The official patch replaces MD5 with SHA256, a cryptographically secure hashing algorithm.

Supply Chain & Package Security

This vulnerability affects the Beego Go package (github.com/beego/beego). Organizations using Beego in their Go applications must update their go.mod file to require version 2.3.4 or later. The package is widely used in Go web services, making this a supply chain risk for any application depending on an affected version.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD) / Adjusted Score: 9.8 (Critical)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

The adjusted CVSS score reflects the ease of exploitation and the severe impact on confidentiality, integrity, and availability. An attacker can forge hashes without authentication, leading to full system compromise.

Deep Dive & Mechanics

The vulnerability lies in Beego's use of MD5 for hashing operations, such as session ID generation, password hashing, or data integrity checks. MD5 is vulnerable to collision attacks, where two distinct inputs produce the same hash. An attacker can:

1. Forge Session Tokens: By generating a collision with a legitimate session hash, an attacker can hijack active sessions.
2. Bypass Authentication: If MD5 is used for password verification, an attacker can create a password that hashes to the same value as a legitimate user's password.
3. Manipulate Data Integrity: If MD5 is used to verify data integrity (e.g., in cookies or request parameters), an attacker can modify data while maintaining the same hash.

The fix in version 2.3.4 replaces all MD5 usage with SHA256, which is currently resistant to collision attacks.

Vulnerable vs. Patched Code

Vulnerable Code (MD5):

import (
    "crypto/md5"
    "fmt"
)

func hashData(data string) string {
    hash := md5.Sum([]byte(data))
    return fmt.Sprintf("%x", hash)
}

Patched Code (SHA256):

import (
    "crypto/sha256"
    "fmt"
)

func hashData(data string) string {
    hash := sha256.Sum256([]byte(data))
    return fmt.Sprintf("%x", hash)
}

The patched code uses crypto/sha256 instead of crypto/md5, providing a cryptographically secure hash.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a vulnerable Beego application (version < 2.3.4) using Docker:

   FROM golang:1.21
   RUN go install github.com/beego/beego@v2.3.3
   

2. Identify endpoints that use MD5 hashing (e.g., session generation, password hashing).

Exploitation Steps:

1. Session Hijacking: Capture a legitimate session hash from a user's cookie.
2. Collision Generation: Use a tool like hashclash to generate a collision:

   # Example using hashclash
   ./hashclash -m md5 -i original_data -o forged_data
   

3. Replace Session Cookie: Send a request with the forged session cookie to hijack the session.

Proof-of-Concept (PoC) Script:

import requests
import hashlib

# Target URL
url = "http://target.com/login"

# Generate MD5 collision (simplified - real collision requires advanced tools)
original_hash = hashlib.md5(b"admin").hexdigest()
forged_data = b"forged_admin"  # In reality, this would be a collision

# Send request with forged session
cookies = {"session": original_hash}
response = requests.get(url, cookies=cookies)
print(response.text)

Blue Team

Detection:

1. Monitor for multiple requests with the same session hash from different IPs.
2. Alert on any use of MD5 in application logs or configuration files.
3. Use static analysis to detect MD5 usage in code.

Mitigation:

1. Immediately upgrade to Beego 2.3.4 or later.
2. If immediate upgrade is not possible, implement a Web Application Firewall (WAF) rule to block requests with suspicious session hashes.
3. Rotate all existing session tokens and force re-authentication for all users.

Indicators of Compromise (IOCs)

• Network: Requests containing MD5-based session cookies (e.g., session=md5hash).
• File: Presence of crypto/md5 import in Go source files.
• Log: Multiple authentication failures followed by a successful login with a forged session.
• Process: Execution of collision generation tools (e.g., hashclash, md5collision).

Detection Engineering

YARA Rule

rule Detect_MD5_Usage_in_Go
{
    meta:
        description = "Detects usage of MD5 hashing in Go source files"
        author = "Valters IT"
        date = "2024-01-01"
        hash = "sha256:abc123"
    strings:
        $md5_import = "crypto/md5"
        $md5_func = "md5.Sum"
        $md5_new = "md5.New"
    condition:
        any of them
}

Sigma Rule

title: Detection of MD5 Hashing in Beego Application
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects the use of MD5 hashing in Beego web framework logs
author: Valters IT
date: 2024-01-01
logsource:
    category: application
    product: beego
detection:
    selection:
        - "MD5"
        - "md5"
        - "crypto/md5"
    condition: selection
falsepositives:
    - Legitimate use of MD5 for non-security purposes (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-55885 - Beego MD5 Hash Collision Attempt"; flow:to_server; content:"session"; nocase; pcre:"/session=[a-f0-9]{32}/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade Beego to version 2.3.4 or later.

   go get github.com/beego/beego@v2.3.4
   

2. Code Review: Scan all Go source files for crypto/md5 usage and replace with crypto/sha256.
3. Session Rotation: Invalidate all existing sessions and force users to re-authenticate.
4. Monitoring: Implement logging and alerting for any MD5-based hashing attempts.
5. Long-term: Adopt a secure development lifecycle that includes cryptographic best practices.

Valters IT
DevSecOps & Cyber Threat Intelligence