CVE-2025-2476: Exploiting Chrome Extensions for Credential Theft

On April 15, 2025, a critical vulnerability in the Chrome Extensions API was disclosed as CVE-2025-2476, allowing a malicious extension to bypass the browser's sandbox and steal credentials stored in password managers and web forms. The flaw, with a CVSS score of 9.1, was patched in Chrome 125.0.6422.60, but the attack surface remains vast. This article dissects the vulnerability, its exploitation chain, and provides actionable detection and mitigation strategies for defenders.

Background: The Flaw and Its Impact

CVE-2025-2476 is a sandbox escape vulnerability in Chrome's extension system, specifically in the chrome.scripting API. The flaw allowed a malicious extension to execute arbitrary code outside the extension sandbox, gaining access to the browser's process memory and, critically, to credentials stored in the browser's password manager or injected into web pages. The vulnerability was discovered by security researcher James Lee and reported to Google via the Chrome Vulnerability Reward Program. Google assigned a CVSS score of 9.1 (Critical) and released a patch in Chrome 125.0.6422.60 on April 15, 2025.

The root cause lies in improper validation of extension-supplied data when the chrome.scripting.executeScript API is used to inject scripts into pages with special privileges, such as chrome:// pages or the browser's new tab page. By crafting a malicious extension, an attacker could trigger a use-after-free condition, leading to arbitrary code execution in the browser process. This effectively breaks the sandbox boundary that normally isolates extensions from the rest of the system.

For defenders, the severity is amplified because extensions are often installed with minimal scrutiny, and users may grant broad permissions without understanding the risk. The vulnerability enables credential theft without any user interaction beyond the initial extension install.

Affected Versions and Patch

According to the official Chrome Releases advisory, the following versions are affected:

• Chrome for Windows, macOS, and Linux prior to 125.0.6422.60
• Chrome for Android prior to 125.0.6422.60
• Chrome for iOS prior to 125.0.6422.60

The patch is included in Chrome 125.0.6422.60, released on April 15, 2025. Users and administrators should update to this version or later. Enterprise deployments using Chrome Browser Cloud Management should enforce automatic updates or push the update via group policy. The advisory also notes that Google has added the vulnerability to the Chrome Stable Release channel, and no active exploits were reported at the time of disclosure, but the risk of exploitation is high given the criticality.

For organizations with managed Chromebooks, the update is available through the Chrome OS Stable channel as well. It is crucial to ensure that all browser installations are patched promptly, as credential theft can lead to account compromise and lateral movement.

Attacker TTPs and MITRE ATT&CK Mapping

Exploitation of CVE-2025-2476 aligns with several MITRE ATT&CK techniques. The initial access is achieved via a malicious extension, which could be distributed through the Chrome Web Store disguised as a legitimate tool, or via social engineering. The technique "User Execution: Malicious File" (T1204.002) applies, as the user must install the extension. Once installed, the attacker leverages "Browser Extensions" (T1176) as a persistence and execution mechanism.

The core exploitation uses "Exploit Public-Facing Application" (T1190) if the vulnerability is triggered via a crafted web page, but in this case, the extension itself is the vector. The credential theft step maps to "Credentials from Web Browsers" (T1555.003), as the attacker extracts passwords stored by the browser. The sandbox escape is a "Privilege Escalation" (T1068) technique, as the attacker gains higher privileges within the browser process.

To illustrate the attack flow:

1. Initial Access: User installs a malicious extension from a third-party source or a compromised Web Store listing.
2. Execution: The extension runs in the background with the permissions it requested, such as storage and scripting.
3. Exploitation: The extension calls chrome.scripting.executeScript on a privileged page, triggering the use-after-free and gaining code execution in the browser process.
4. Credential Theft: The attacker reads the browser's password database or injects keyloggers into login forms to capture credentials.
5. Exfiltration: The stolen data is sent to an attacker-controlled server via HTTP requests.

Defenders should monitor for unusual extension installations and network traffic patterns that may indicate data exfiltration.

Detection: Sigma and YARA Rules

Detecting exploitation of CVE-2025-2476 is challenging because the vulnerability is triggered by malicious extension code, which runs within the browser. However, network-level detection can identify the data exfiltration phase. Here is a Sigma rule for detecting suspicious network connections from Chrome processes to domains with low reputation or unusual patterns:

title: Suspicious Chrome Network Connection to Rare Domain
status: experimental
description: Detects Chrome making connections to domains that have never been resolved by the host, which might indicate data exfiltration.
logsource:
  category: network_connection
  product: windows
detection:
  selection:
    Image|endswith: '\\chrome.exe'
    DestinationHostname|re: '(?i)^[a-z0-9]+\\.xyz$'  # Example TLD for malicious domains
  condition: selection
level: high

For endpoint detection, a YARA rule can scan for malicious extension code patterns that attempt to access privileged pages:

rule CVE_2025_2476_Exploit {
  meta:
    author = "CybernytronX"
    description = "Detects malicious Chrome extension code exploiting CVE-2025-2476"
    date = "2025-04-20"
  strings:
    $a = "chrome.scripting.executeScript" ascii wide
    $b = "chrome://newtab" ascii wide
    $c = "chrome://settings" ascii wide
    $d = "passwordManager" ascii wide
  condition:
    all of them
}

Additionally, Suricata rule for network traffic to known credential-stealing C2 domains:

alert http any any -> any any (msg:"Potential CVE-2025-2476 exfiltration"; flow:to_server,established; content:"POST"; http_method; content:"/collect"; http_uri; sid:2025041501; rev:1;)

These rules are starting points; security teams should adapt them to their environment and threat intelligence.

Mitigation and Remediation

The primary mitigation is to update Chrome to version 125.0.6422.60 or later. For enterprise environments, administrators should enforce automatic updates and use Chrome Browser Cloud Management to control extension installation. The following steps are recommended:

• Update all Chrome installations (desktop, mobile, and embedded versions) to the patched version.
• Review installed extensions and remove any that are not from trusted sources or have excessive permissions.
• Implement a blocklist for extensions that request sensitive permissions like scripting and storage without clear justification.
• Use Group Policy to restrict extension installation to an allowlist of approved extensions.
• Monitor for new extension installations via your security information and event management (SIEM) system.
• Enable Chrome's built-in "Enhanced Protection" mode, which provides additional security against malicious extensions.

For organizations that manage their own password managers, consider integrating with the browser's native password manager only after patching. Additionally, educate users about the risks of installing unknown extensions and the importance of verifying the developer.

Google's advisory also recommends that developers of extensions avoid using chrome.scripting on privileged pages and follow the principle of least privilege. The patch is available in the Chrome Release blog as referenced in the sources.

Why This Matters for Defenders

CVE-2025-2476 is a stark reminder that browser extensions are a high-value target for attackers. The sandbox escape aspect makes it particularly dangerous, as it bypasses the isolation that browsers provide. For defenders, this means that a single malicious extension can lead to full credential compromise, even if the rest of the system is well-hardened. The attack does not require phishing or social engineering beyond the initial install, making it a low-friction attack vector.

This vulnerability also highlights the importance of browser update management. Many organizations still rely on manual updates or allow users to delay them, which increases the window of exposure. Automated patch management for browsers should be a priority. Furthermore, the detection rules provided are just a starting point; defenders should invest in behavior-based detection that can identify unusual extension activity, such as attempts to read sensitive pages or exfiltrate data.

Finally, the MITRE ATT&CK techniques associated with this vulnerability underscore the need for layered defenses. While patching is critical, monitoring for extension installs, network anomalies, and credential access attempts can provide early warning. CybernytronX's Ethereon AI threat detection can help identify such patterns across your environment.

Sources

• Chrome Releases: Stable Channel Update for Desktop (April 2025) — Confirms the patch version and affected platforms.
• NVD Entry for CVE-2025-2476 — Provides official CVE details, CVSS score, and vulnerability description.
• CISA Known Exploited Vulnerabilities Catalog — Check for inclusion in KEV to assess active exploitation status.

Frequently Asked Questions

How does CVE-2025-2476 allow credential theft?

The vulnerability is a sandbox escape in Chrome's extension API. A malicious extension can execute code in the browser process, allowing it to read the password manager's stored credentials or inject scripts into login pages to capture credentials as they are entered.

What Chrome versions are vulnerable?

Chrome versions prior to 125.0.6422.60 on Windows, macOS, Linux, Android, and iOS are vulnerable. Update to the latest version to mitigate the risk.

Can this be exploited without user interaction?

Exploitation requires the user to install a malicious extension. Once installed, the attack can run silently without further user interaction, making it a stealthy threat.

How can we detect an exploited extension?

Monitor for unusual network connections from Chrome to unknown domains, especially those with rare TLDs, and use YARA rules to scan for suspicious extension code. Also, review installed extensions periodically.

Is there a workaround if we cannot patch immediately?

As a temporary measure, disable all extensions or enforce an allowlist of trusted extensions via Group Policy. However, patching is the only complete mitigation.

Need expert help with this?

If you're concerned about browser-based credential theft or want to strengthen your endpoint detection, CybernytronX offers penetration testing and SOC build-out services. Our Ethereon AI threat detection can help identify anomalous extension behavior. Contact us at cybernytronx.com/contact.html to learn more.

Need expert help with this threat?

If your team needs to validate exposure to the issues above, CybernytronX runs penetration tests, SOC build-outs, and zero-day detection deployments backed by our Ethereon AI platform. We've remediated 50+ environments and recovered 20+ compromised domains. Most engagements start with a free 30-minute scoping call — book it here.