CVE-2019-3701 in Linux
Summary
by MITRE
An issue was discovered in can_can_gw_rcv in net/can/gw.c in the Linux kernel through 4.19.13. The CAN frame modification rules allow bitwise logical operations that can be also applied to the can_dlc field. Because of a missing check, the CAN drivers may write arbitrary content beyond the data registers in the CAN controller's I/O memory when processing can-gw manipulated outgoing frames. This is related to cgw_csum_xor_rel. An unprivileged user can trigger a system crash (general protection fault).
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Analysis
by VulDB Data Team • 06/23/2023
The vulnerability identified as CVE-2019-3701 resides within the Linux kernel's CAN (Controller Area Network) gateway implementation, specifically in the can_can_gw_rcv function located in net/can/gw.c. This flaw affects Linux kernel versions through 4.19.13 and represents a critical security issue that can lead to system instability and potential denial of service conditions. The CAN protocol is widely used in automotive and industrial control systems for communication between embedded devices, making this vulnerability particularly concerning for environments where kernel-level security is paramount.
The technical flaw stems from insufficient validation within the CAN frame modification rules that govern how bitwise logical operations are processed. Specifically, the implementation fails to properly validate the can_dlc (CAN data length) field when applying bitwise operations, allowing maliciously crafted CAN frames to manipulate this field in ways that bypass normal bounds checking. This missing validation creates a condition where the CAN drivers can write data beyond the legitimate data registers in the CAN controller's I/O memory space. The vulnerability is particularly insidious because it operates at the kernel level, where memory corruption can lead to immediate system crashes or more subtle security implications.
The operational impact of this vulnerability extends beyond simple system crashes, as it represents a classic buffer overflow condition that can be exploited by unprivileged users to trigger general protection faults. According to CWE-121, this vulnerability manifests as a stack-based buffer overflow in the kernel space, where the absence of proper bounds checking allows for arbitrary memory writes. The exploitation requires only basic user privileges, making it particularly dangerous in environments where untrusted users might have access to CAN network interfaces. This aligns with ATT&CK technique T1068 which describes the exploitation of vulnerabilities in kernel space to gain elevated privileges or cause system instability.
The vulnerability is directly related to cgw_csum_xor_rel functionality, which handles checksum operations during CAN frame processing. When an attacker crafts malicious CAN frames that manipulate the data length field, the kernel's gateway processing logic can be tricked into writing beyond allocated memory regions. This creates a scenario where the kernel's memory management can be compromised, potentially leading to information disclosure, system crashes, or in more sophisticated attack scenarios, privilege escalation. The absence of proper input validation for the can_dlc field represents a fundamental security oversight that violates the principle of least privilege and proper bounds checking.
Mitigation strategies for CVE-2019-3701 should include immediate patching of affected Linux kernel versions to the patched releases that address the missing validation checks in the CAN gateway implementation. Organizations should also implement network segmentation to limit access to CAN interfaces, particularly in automotive and industrial environments where these vulnerabilities could be exploited to compromise critical systems. Additionally, monitoring for anomalous CAN frame patterns and implementing proper access controls for CAN network interfaces can help detect and prevent exploitation attempts. The fix typically involves adding proper bounds checking for the can_dlc field before allowing bitwise operations to be applied, ensuring that modifications to this field cannot result in memory corruption beyond the intended data buffer boundaries.