CVE-2024-35856 in Linux
Summary
by MITRE • 05/17/2024
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: btusb: mediatek: Fix double free of skb in coredump
hci_devcd_append() would free the skb on error so the caller don't have to free it again otherwise it would cause the double free of skb.
Reported-by : Dan Carpenter
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability CVE-2024-35856 represents a critical double free condition in the Linux kernel's Bluetooth subsystem, specifically within the btusb driver for Mediatek chipsets. This flaw exists in the hci_devcd_append() function which handles Bluetooth core dump operations. The issue manifests when error conditions occur during Bluetooth device communication processing, where the function autonomously frees the socket buffer (skb) structure but fails to properly manage the reference count or state tracking that would prevent subsequent cleanup attempts by the calling code. This creates a scenario where the same memory location gets freed twice, leading to potential memory corruption and system instability. The vulnerability was identified through careful code analysis and reported by security researcher Dan Carpenter, highlighting a fundamental flaw in resource management within the kernel's Bluetooth stack.
The technical implementation of this vulnerability stems from improper memory management within the Bluetooth subsystem's core dump handling mechanism. When hci_devcd_append() encounters an error condition, it executes a skb_free() operation on the socket buffer, but the calling code remains unaware of this automatic cleanup and proceeds to attempt another free operation on the same memory location. This classic double free vulnerability falls under CWE-415, which specifically addresses the freeing of memory a second time, and represents a critical flaw in the kernel's memory management subsystem. The flaw is particularly concerning because it operates within the kernel space where such memory corruption can lead to privilege escalation or system crashes. The Mediatek-specific implementation adds complexity as it involves chipset-specific Bluetooth driver code that interfaces with the generic Bluetooth subsystem through the btusb driver module.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable more severe security implications within kernel environments. When a double free occurs in kernel space, it can be exploited to manipulate kernel memory layout, potentially allowing attackers with local access to escalate privileges or cause denial of service conditions that could affect the entire system. The vulnerability affects systems running Linux kernels with Bluetooth support, particularly those utilizing Mediatek Bluetooth chipsets through the btusb driver. In practical attack scenarios, an attacker could trigger the error condition through malformed Bluetooth communication packets or device interactions, leading to memory corruption that might be exploitable for privilege escalation. The impact is especially significant in embedded systems or IoT devices that rely heavily on Bluetooth connectivity and operate with elevated privileges.
Mitigation strategies for CVE-2024-35856 primarily involve applying the official kernel patches that address the double free condition by ensuring proper state management within the hci_devcd_append() function. System administrators should prioritize updating their Linux kernels to versions that include the fix, which typically involves modifying the function to track whether the skb has already been freed or implementing proper error handling that prevents redundant cleanup operations. Organizations should also implement monitoring for unusual Bluetooth communication patterns that might indicate exploitation attempts and consider disabling Bluetooth functionality on systems where it is not essential. The fix aligns with ATT&CK technique T1059.003 for command and scripting interpreter usage, as exploitation might involve crafting specific Bluetooth commands to trigger the vulnerability. Additionally, system hardening measures including kernel lockdown features and proper access controls should be implemented to limit potential exploitation surfaces and reduce the attack surface for such memory corruption vulnerabilities.