CVE-2024-1240

Executive Summary

CVE-2024-1240 is an open redirection vulnerability in pyload/pyload version 0.5.0. The flaw exists in the login functionality, where the next parameter is not properly sanitized. An attacker can craft a malicious link that, when clicked by an authenticated user, redirects them to an attacker-controlled external site. This can be leveraged for phishing campaigns, credential harvesting, or other social engineering attacks. The vulnerability has a CVSS score of 4.6 (Medium) and is fixed in pyload-ng 0.5.0b3.dev79. No public exploit code or Nuclei templates are available at this time.

Supply Chain & Package Security

This vulnerability affects the PyPI package pyload. Users should update to the patched version pyload-ng 0.5.0b3.dev79 or later. The open redirection flaw does not directly compromise the package supply chain, but it can be used in phishing attacks targeting users of the application.

CVSS Breakdown & Threat Level

• CVSS Score: 4.6 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

The threat level is considered Medium due to the requirement for user interaction and the limited impact on confidentiality and integrity. However, the open redirection can be a powerful tool in phishing campaigns.

Deep Dive & Mechanics

The vulnerability resides in the login endpoint of pyload. When a user logs in, the application uses a next parameter to redirect the user to a specified page after successful authentication. The code does not validate whether the next parameter is a relative path or an absolute URL pointing to an external domain. An attacker can exploit this by crafting a URL like:

https://vulnerable-pyload-instance/login?next=https://attacker-controlled-site.com

When a user clicks this link and logs in, they are redirected to the attacker's site, which may mimic the legitimate login page to steal credentials or other sensitive information.

Vulnerable vs. Patched Code

Vulnerable Code (pyload 0.5.0):

# login handler
def login(self, username, password, next):
    # authentication logic
    if authenticated:
        return redirect(next)

Patched Code (pyload-ng 0.5.0b3.dev79):

# login handler
def login(self, username, password, next):
    # authentication logic
    if authenticated:
        # Validate that 'next' is a relative path
        if next and not next.startswith('/'):
            next = '/'
        return redirect(next)

The patch ensures that the next parameter must start with a forward slash (/), preventing redirection to external domains.

Exploitation & Lab Setup

Red Team

1. Setup: Deploy a vulnerable pyload instance (version 0.5.0) in a lab environment.
2. Craft Exploit URL: Create a URL that includes a malicious next parameter:

   http://vulnerable-pyload/login?next=http://attacker.com/phishing
   

3. Deliver Payload: Send the crafted URL to a victim via email or social engineering.
4. Execute: When the victim logs in, they are redirected to the attacker's site.

Blue Team

1. Detection: Monitor for unusual next parameters in login requests. Look for absolute URLs or external domains.
2. Mitigation: Apply the patch by updating to pyload-ng 0.5.0b3.dev79 or later.
3. Hunting: Search logs for login requests with next parameters containing external URLs.

Indicators of Compromise (IOCs)

• Network: HTTP requests to /login with a next parameter containing an external domain.
• Logs: Login events where the next parameter is not a relative path.
• URL Pattern: */login?next=http://* or */login?next=https://*

Detection Engineering

YARA Rule

rule CVE_2024_1240_Open_Redirect {
    meta:
        description = "Detects open redirection attempts in pyload login"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-1240"
    strings:
        $s1 = "next="
        $s2 = "http://"
        $s3 = "https://"
    condition:
        all of ($s1, $s2) or all of ($s1, $s3)
}

Sigma Rule

title: Pyload Open Redirection Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2024-1240 open redirection in pyload
author: Valters IT
date: 2024/01/01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: "next=http://"
    condition: selection
falsepositives:
    - Legitimate use of external redirects (rare)
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-1240 Pyload Open Redirection Attempt"; flow:to_server; content:"/login"; http_uri; content:"next="; http_uri; pcre:"/next=https?:\/\//Ui"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Update pyload to version 0.5.0b3.dev79 or later.
2. Workaround: If immediate update is not possible, implement a reverse proxy rule to block next parameters containing external URLs.
3. Long-term: Ensure all redirect parameters are validated to only allow relative paths.
4. Monitoring: Enable logging of all login attempts and monitor for suspicious next parameters.

Valters IT