CVE-2021-34693 in Linux
Summary
by MITRE • 06/15/2021
net/can/bcm.c in the Linux kernel through 5.12.10 allows local users to obtain sensitive information from kernel stack memory because parts of a data structure are uninitialized.
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Analysis
by VulDB Data Team • 06/18/2021
The vulnerability identified as CVE-2021-34693 resides within the Linux kernel's CAN (Controller Area Network) subsystem, specifically in the bcm.c file responsible for handling broadcast manager operations. This issue affects Linux kernel versions through 5.12.10 and represents a classic case of uninitialized memory exposure that can lead to information disclosure. The vulnerability occurs when certain data structures used by the broadcast manager are not properly initialized before being populated with data, creating potential pathways for sensitive information leakage from kernel memory space.
The technical flaw manifests in the uninitialized data structure handling within the kernel's CAN subsystem where specific fields within a data structure are left in an undefined state. When the broadcast manager processes CAN messages, it relies on certain data structures that contain uninitialized memory regions. Local users can exploit this by crafting specific CAN messages or broadcast manager operations that cause the kernel to return portions of uninitialized stack memory to userspace applications. This uninitialized memory may contain remnants of previous kernel operations, sensitive data, or system configuration information that should not be accessible to unprivileged users.
The operational impact of this vulnerability extends beyond simple information disclosure as it provides attackers with potential insights into kernel memory layout, system state, and possibly sensitive operational data. Since the vulnerability is local in nature, an attacker must already have user-level access to the system to exploit it, but the information obtained can be leveraged for more sophisticated attacks including kernel exploitation techniques or bypassing security mechanisms. The exposure of kernel stack memory can reveal memory addresses, kernel data structures, or other sensitive information that could aid in developing more advanced attacks against the system. This type of information disclosure vulnerability aligns with CWE-1280 which specifically addresses uninitialized memory exposure in kernel contexts and represents a significant concern for embedded systems and automotive applications where CAN networks are prevalent.
Mitigation strategies for CVE-2021-34693 primarily involve applying the official kernel patches released by the Linux kernel security team, which properly initialize the affected data structures before use. System administrators should prioritize updating their kernel installations to versions 5.12.11 or later where this vulnerability has been addressed. Additionally, implementing proper access controls and limiting local user privileges can reduce the attack surface, though this does not eliminate the vulnerability itself. Network segmentation and monitoring for unusual CAN message patterns may also help detect potential exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1059.001 for command and scripting interpreter and T1566.001 for spearphishing attachment, as exploitation typically requires local user access and could be part of broader attack chains targeting automotive or industrial control systems where CAN networks are utilized. Organizations should also consider implementing kernel memory protection mechanisms and regular security audits of their kernel configurations to prevent similar issues from arising in other subsystems.