Update: As of June 2024, a critical Android vulnerability tracked as CVE-2024-40676 has been made public, outlining a method for local attackers to abuse the AccountManagerService. This bug enables installation of apps without the user's knowledge and escalates the attacker’s privileges, while requiring no particular permissions that aren’t already present on most user devices. Weaponsing this flaw does not require any user interaction.

What is CVE-2024-40676?

CVE-2024-40676 is a confused deputy vulnerability stemming from insecure intent handling in checkKeyIntent in AccountManagerService.java. The flaw arises when the service fails to verify that the app requesting install permissions is trustworthy, allowing a less-privileged or malicious app to trick AccountManagerService into launching an intent with escalated privileges. This essentially lets an attacker bypass standard security barriers and install unauthorized APKs.

How the Exploit Works (Plain English)

Normally, apps can’t install other apps without clear user consent—like you pressing “Install” in the Play Store. Some Android system components, however, *can* launch installation activities since they operate with system-level privileges.

In the vulnerable version, AccountManagerService will honor any request for certain "key intent" activities (such as installing or authenticating accounts) *without* properly checking if the calling app itself is authorized. Through an attack known as the "confused deputy problem", a malicious app submits a specially crafted intent. The system component, mistaking the request for a valid one, processes it using its broadened permissions.

Sample Code Snippet: Core Vulnerable Logic

This is a representative, simplified snippet from AccountManagerService.java (see the bug’s AOSP commit):

// Vulnerable code logic
private void checkKeyIntent(Intent intent, int callerUid) {
    // ... some validation ...
    PackageManager pm = mContext.getPackageManager();
    ResolveInfo ri = pm.resolveActivity(intent, );
    if (ri != null) {
        // Attacker can now escalate intent with install permissions
        mContext.startActivityAsUser(intent, UserHandle.SYSTEM);
    }
    // No robust check for caller identity or intent target!
}

Problem: There’s no firm verification that the intent’s real sender is trustworthy. The system service simply accepts and acts on the promoted intent.

Exploit Steps (for Education)

1. Malicious App Preparation: The attacker develops an app that crafts a malicious intent that requests AccountManager-related privileges (such as installing an APK).
2. Submit Malicious Intent: The app submits this intent to the vulnerable service (AccountManagerService).
3. Service Escalation: The system service, running with higher privileges, accepts and processes the intent—installing the attacker’s APK *without* any user interface or prompt.
4. Looper: The attacker’s payload app is installed, granting them deeper access or persistence on the device.

Proof-of-Concept (PoC) Example (simplified)

// Malicious app's code
Intent maliciousIntent = new Intent();
maliciousIntent.setAction(Intent.ACTION_INSTALL_PACKAGE);
maliciousIntent.setData(Uri.fromFile(new File("/sdcard/evil.apk")));
maliciousIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

// Send this intent to AccountManagerService using a bound service or reflection hack.
sendAccountManagerIntent(maliciousIntent);

Note: Modern Android versions may have patched components or bolster checks. Test only on permitted devices, e.g., AVD with vulnerable Android images.

Stealth Persistence: Malicious actors can install more persistent malware, rootkits, or spyware.

- Escalated Privileges: Attackers can chain this with other exploits to fully compromise an Android OS, exfiltrate sensitive data, or maintain firmware-level access.

Mitigation

- Update your device: Android Security Bulletin (June 2024) fixes this bug. See official patch.
- App code best practices: If your app uses AccountManagerService, ensure you verify calling UIDs and intent origins before acting on elevated requests.
- General user advice: Avoid sideloading apps, and ensure auto-updates are enabled for your system.

References

- Google Android Security Bulletin June 2024
- NVD entry for CVE-2024-40676
- AOSP Commit (examples of previous intent checks)
- Confused Deputy Problem (Wikipedia)

Summary

CVE-2024-40676 is a critical privilege escalation bug in Android, requiring no user input to exploit, and allows full app installs without notification. If your devices or apps rely on AccountManagerService, patch immediately and review privilege boundaries for all indirect intent handling. Never trust third-party apps with permissions you can't independently verify.

Stay safe—and always keep your OS up to date!

*This analysis was prepared exclusively to explain the unique mechanics and risks involved with CVE-2024-40676. Reach out to your vendor for patching details or visit the Android security portal for ongoing updates.*

Timeline

Published on: 01/28/2025 20:15:49 UTC
Last modified on: 02/06/2025 16:15:37 UTC