CVE-2024-0041 is a recently disclosed vulnerability affecting Android system components, specifically inside SystemStatusAnimationSchedulerImpl.kt. The risk? A logic flaw and race condition could let malicious local apps take advantage of insufficient checks, failing to properly remove the "persistent dot" (an indicator for status events)—potentially leading to local privilege escalation without needing extra permissions or user interaction.

In this post, we’ll break down the vulnerability, show code snippets, explain how it’s exploited, and link to useful references. We’ll keep language simple and easy to follow.

What is the "Persistent Dot"?

Many Android devices show a small dot in the status bar when certain system events occur (such as microphone/camera usage). The SystemStatusAnimationSchedulerImpl.kt file manages when that dot appears and disappears.

Ordinarily, the system uses a function called removePersistentDot to remove the dot when it’s no longer needed.

The Bug: Race Condition in removePersistentDot

Race conditions happen when two or more pieces of code run simultaneously, leading to unexpected results (for example, a security check getting bypassed because of the timing of events). In this case, the race condition lies in removePersistentDot, which is tasked with updating or removing the dot.

Here’s a simplified version of what the vulnerable code might look like (some details changed for clarity):

// SystemStatusAnimationSchedulerImpl.kt

class SystemStatusAnimationSchedulerImpl {
    private var persistentDotVisible: Boolean = false
    private val lock = Any()

    fun removePersistentDot() {
        synchronized(lock) {
            if (persistentDotVisible) {
                // do some cleanup
                persistentDotVisible = false
                notifyStatusChanged()
            }
        }
    }

    fun showPersistentDot() {
        synchronized(lock) {
            persistentDotVisible = true
            // code to display the dot
        }
    }
}

Logic error:
If two processes call removePersistentDot() and showPersistentDot() in rapid succession, it’s possible for the state of persistentDotVisible to get out of sync, leading to a situation where the dot appears permanently — or worse, is incorrectly removed or never shown. This logic bug comes from assuming there is only a single-threaded access path or from not checking possible state after delay in synchronized block. Through careful timing, a malicious app could use this to escalate privileges or hide its activity.

Here’s how an attacker could abuse the race condition (at a high level)

1. The attacker runs code that rapidly calls showPersistentDot() and removePersistentDot() from multiple threads.

The system fails to remove the persistent dot, or leaves it visible beyond its legitimate context.

4. This can result in a local app overwriting or misleading user/system about critical system status (for example, hiding the dot while using a privileged resource).
5. Since no additional permissions or user interaction are required, any app running locally could attempt to trigger the race.

Example (Pseudo-code in an exploit app)

fun exploitRaceCondition(scheduler: SystemStatusAnimationSchedulerImpl) {
    val t1 = Thread { repeat(100) { scheduler.showPersistentDot() } }
    val t2 = Thread { repeat(100) { scheduler.removePersistentDot() } }
    t1.start()
    t2.start()
    t1.join()
    t2.join()
}

By flooding the scheduler with rapid conflicting requests, the attacker can potentially win the race and get the system into a compromised or inconsistent state.

Local escalation of privilege:

The attacker could tamper with status indicators without proper authorization, possibly hiding critical notifications or misrepresenting system status.

Persistence without permission:

Malicious code can make the “dot” stick around or disappear without system approval, possibly misleading users.

Update your device.

Google has issued a security patch to fix CVE-2024-0041 in supported Android versions.

Developers: Use stronger synchronization.

Double-check your multi-threaded code and avoid making assumptions about access order. Consider atomic flags or robust state tracking.

References

- Android Security Bulletin - June 2024
- Google Issue Tracker: 309734567 (CVE-2024-0041) _(Check if public)_
- Mitre CVE Database - CVE-2024-0041

Conclusion

CVE-2024-0041 is a great example of how simple logic errors in multi-threaded code can have real-world security consequences. In this case, a race condition in removePersistentDot makes it possible for unprivileged local attackers to manipulate system UI indicators, potentially escalating local privileges. No extra permissions or interaction are required.

Keep your devices updated, and if you write multi-threaded code, remember: verify your state, test with concurrent scenarios, and patch early!


*For more technical details and PoC discussion, check the above references or contact your device vendor for patches.*

Timeline

Published on: 02/16/2024 02:15:51 UTC
Last modified on: 08/26/2024 17:35:02 UTC