CVE-2025-55305

Executive Summary

CVE-2025-55305 is a high-severity vulnerability in the Electron framework that allows an attacker to bypass ASAR integrity validation by modifying resources within the ASAR archive. This vulnerability only affects applications that have both the embeddedAsarIntegrityValidation and onlyLoadAppFromAsar fuses enabled. An attacker with local access to the system can modify the application's ASAR archive, potentially injecting malicious code or altering application behavior. The vulnerability has a CVSS score of 6.1 and is currently unpatched in affected versions.

Supply Chain & Package Security

This vulnerability is specific to the Electron framework, which is distributed via npm as the electron package. Applications that bundle Electron and enable the vulnerable fuses are at risk. The supply chain risk is moderate, as the vulnerability requires local access and specific fuse configuration. However, once exploited, it can lead to arbitrary code execution within the application's context.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Local (L) - Requires local access to the system.
• Attack Complexity (AC): Low (L) - No special conditions required.
• Privileges Required (PR): Low (L) - Attacker needs low-level privileges.
• User Interaction (UI): None (N) - No user interaction required.
• Scope (S): Unchanged (U) - The vulnerability does not affect other components.
• Confidentiality (C): High (H) - Potential for data exfiltration.
• Integrity (I): High (H) - Application behavior can be modified.
• Availability (A): None (N) - No impact on availability.

Threat Level: High. While the attack vector is local, the low complexity and potential for significant impact make this a serious concern for applications with the vulnerable configuration.

Deep Dive & Mechanics

The vulnerability lies in the ASAR integrity validation mechanism. Electron applications can be packaged into ASAR archives, which are essentially tar-like archives containing the application's resources. The embeddedAsarIntegrityValidation fuse enables integrity checking of the ASAR archive, while onlyLoadAppFromAsar ensures that the application only loads resources from the ASAR archive.

The flaw occurs when the application loads resources from the ASAR archive. The integrity validation is not properly enforced during resource loading, allowing an attacker to modify the ASAR archive's contents after the initial validation. This can be achieved by:

1. Modifying the ASAR file directly: An attacker with write access to the application's installation directory can modify the ASAR archive.
2. Using symbolic links or hard links: An attacker could create symbolic links within the ASAR archive to point to malicious files.
3. Race condition: In some cases, a race condition between validation and loading could be exploited.

The impact is that an attacker can inject arbitrary JavaScript code into the application, leading to:

• Data exfiltration: Stealing sensitive data from the application.
• Privilege escalation: If the application runs with elevated privileges.
• Persistence: Modifying the application to maintain access.

Vulnerable vs. Patched Code

The vulnerable code path is in the ASAR resource loading logic. The patched version ensures that integrity validation is performed every time a resource is loaded from the ASAR archive.

Vulnerable Code (Conceptual):

// Vulnerable: Integrity check only at startup
function loadResource(path) {
  // No integrity check here
  return fs.readFileSync(path);
}

Patched Code (Conceptual):

// Patched: Integrity check on every resource load
function loadResource(path) {
  if (!validateIntegrity(path)) {
    throw new Error('Integrity check failed');
  }
  return fs.readFileSync(path);
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to the target system.
• Write access to the application's installation directory.
• The application must have both embeddedAsarIntegrityValidation and onlyLoadAppFromAsar fuses enabled.

Exploitation Steps:

1. Identify the target application: Find an Electron application with the vulnerable configuration.
2. Locate the ASAR archive: Typically found in the application's resources directory (e.g., app.asar).
3. Extract the ASAR archive:

   npx asar extract app.asar app
   

4. Modify the application code: Inject malicious JavaScript into one of the application's files.

   // Example: Inject a backdoor
   require('child_process').exec('calc.exe');
   

5. Repack the ASAR archive:

   npx asar pack app app.asar
   

6. Replace the original ASAR archive: Overwrite the original app.asar with the modified one.
7. Restart the application: The malicious code will execute.

Blue Team

Detection:

• Monitor for modifications to ASAR files in application directories.
• Use file integrity monitoring (FIM) tools to detect changes to ASAR archives.
• Monitor for processes spawning unexpected child processes from Electron applications.

Prevention:

• Ensure the application is updated to a patched version.
• If patching is not possible, disable the embeddedAsarIntegrityValidation and onlyLoadAppFromAsar fuses.
• Implement application whitelisting to prevent unauthorized modifications.
• Use endpoint detection and response (EDR) solutions to detect exploitation attempts.

Indicators of Compromise (IOCs)

• File Hashes: Modified ASAR files with unexpected hashes.
• Process Behavior: Electron processes spawning unexpected child processes (e.g., cmd.exe, powershell.exe).
• Network Connections: Unexpected outbound connections from Electron applications.
• File System Changes: Creation of symbolic links or hard links within application directories.
• Registry Changes: Modifications to application configuration that enable the vulnerable fuses.

Detection Engineering

YARA Rule

rule CVE_2025_55305_ASAR_Modification {
    meta:
        description = "Detects modified ASAR files indicating CVE-2025-55305 exploitation"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-55305"
    strings:
        $asar_magic = { 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 } // ASAR header magic
        $suspicious_js = "require('child_process')" nocase
        $suspicious_eval = "eval(" nocase
    condition:
        $asar_magic at 0 and (#suspicious_js > 0 or #suspicious_eval > 0)
}

Sigma Rule

title: CVE-2025-55305 - ASAR Integrity Bypass
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential exploitation of CVE-2025-55305 via ASAR file modification
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-55305
logsource:
    category: file_event
    product: windows
detection:
    selection:
        EventID: 11
        TargetFilename|endswith: '.asar'
        Image|endswith: '\\asar.exe'
    condition: selection
falsepositives:
    - Legitimate application updates
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2025-55305 - Potential ASAR Integrity Bypass Exploitation";
    flow:to_server,established;
    content:"asar"; http_uri;
    content:"integrity"; http_uri;
    sid:1000001;
    rev:1;
    reference:cve,2025-55305;
)

Remediation & Mitigation

Immediate Actions:

1. Update Electron: Upgrade to versions 35.7.5, 36.8.1, 37.3.1, or 38.0.0-beta.6 or later.
2. Disable Vulnerable Fuses: If patching is not immediately possible, disable the embeddedAsarIntegrityValidation and onlyLoadAppFromAsar fuses in the application's configuration.
3. Restrict Access: Limit write access to application installation directories to trusted users only.

Long-term Mitigations:

1. Code Signing: Implement code signing for ASAR archives to prevent tampering.
2. File Integrity Monitoring: Deploy FIM solutions to monitor for unauthorized changes to ASAR files.
3. Application Hardening: Use Electron's security features, such as context isolation and sandboxing, to limit the impact of exploitation.
4. Regular Audits: Conduct regular security audits of Electron applications to identify and remediate vulnerabilities.

Valters IT Signature This report was generated by Valters IT Cyber Threat Intelligence Division. For further analysis or incident response assistance, contact us at contact@valters-it.com.