CVE-2021-0883 - A Deep Dive into PVRSRVBridgeCacheOpQueue Integer Overflow and Possible Privilege Escalation in PowerVR Kernel Driver

In today's highly connected world, security is of the utmost importance, especially when it comes to mobile devices. The Android operating system, which runs on a majority of smartphones, is no exception - ensuring its security must be a top priority.

One particular security issue, identified as CVE-2021-0883, has recently caught our attention. This vulnerability lies in the PVRSRVBridgeCacheOpQueue of the PowerVR kernel driver, and could potentially lead to a local escalation of privileges on an Android device. In this article, we will take a deep dive into the technical details of this vulnerability, discussing possible exploit scenarios and how it can be mitigated.

Vulnerability Details

The vulnerability specifically targets the function PVRSRVBridgeCacheOpQueue in PowerVR kernel driver. A crucial size check is missing in the implementation of this function, which can result in an integer overflow and out-of-bounds heap access. This vulnerability, if successfully exploited, could lead to local escalation of privilege with no additional execution privileges needed. Furthermore, user interaction is not required for exploitation.

Here is a code snippet representing the affected function

IMG_INT
PVRSRVBridgeCacheOpQueue(IMG_UINT32 ui32DispatchTableEntry,
                 PVRSRV_BRIDGE_IN_CACHEOPQUEUE *psCacheOpQueueIN,
                 PVRSRV_BRIDGE_OUT_CACHEOPQUEUE *psCacheOpQueueOUT,
                 CONNECTION_DATA *psConnection)
{
    ...
    for (ui32Loop = ; ui32Loop < psCacheOpQueueIN->ui32NumCacheOpVal; ui32Loop++)
    {
        CacheOpQueues(ui32Loop, hCacheOpQueue,
                        psCacheOpQueueIN->sCacheOpVal[ui32Loop].ui64ExecuteTime,
                        psCacheOpQueueIN->sCacheOpVal[ui32Loop].ui32NumCacheOpRanges,
                        psCacheOpQueueIN->sCacheOpVal[ui32Loop].sCacheOpRange);
    }
    ...
}

In the above code snippet, we can see that the PVRSRVBridgeCacheOpQueue function is iterating through a loop that is bounded by the ui32NumCacheOpVal value, which is user-controlled. However, there is no size check for the sCacheOpVal array, which could lead to an integer overflow if a sufficiently large value is passed as ui32NumCacheOpVal. This could ultimately result in out-of-bounds heap access, potentially compromising the security of the device.

For a more detailed look at this vulnerability, refer to the original disclosure here: CVE-2021-0883 - NVD or the Android security bulletin: Android Security Bulletin - CVE-2021-0883

To exploit this vulnerability, an attacker would need to

1. Craft an appropriate PVRSRV_BRIDGE_IN_CACHEOPQUEUE structure with a strategically chosen ui32NumCacheOpVal value.

Exploit the out-of-bounds heap access caused by the integer overflow.

The attacker could potentially leverage the out-of-bounds heap access to gain escalated privileges on the targeted device, without the need for any additional execution privileges or user interaction.

Mitigation and Conclusion

As demonstrated, CVE-2021-0883 is a critical vulnerability that could potentially lead to privilege escalation on a vulnerable Android device. To protect against a potential exploit, it's crucial to keep your device's software up-to-date, as OEMs and Google will push out security patches aimed at addressing known vulnerabilities like this one.

Additionally, developers working with the PowerVR kernel driver for the Android operating system should be mindful of the missing size check in PVRSRVBridgeCacheOpQueue, and implement appropriate security measures to prevent integer overflow and out-of-bounds heap access. By staying informed and taking appropriate actions to mitigate these types of vulnerabilities, we can all contribute to a safer and more secure Android ecosystem.

Timeline

Published on: 04/19/2023 20:15:00 UTC
Last modified on: 04/27/2023 20:32:00 UTC