CVE-2022-2503 in Linux
Summary
by MITRE • 08/12/2022
Dm-verity is used for extending root-of-trust to root filesystems. LoadPin builds on this property to restrict module/firmware loads to just the trusted root filesystem. Device-mapper table reloads currently allow users with root privileges to switch out the target with an equivalent dm-linear target and bypass verification till reboot. This allows root to bypass LoadPin and can be used to load untrusted and unverified kernel modules and firmware, which implies arbitrary kernel execution and persistence for peripherals that do not verify firmware updates. We recommend upgrading past commit 4caae58406f8ceb741603eee460d79bacca9b1b5
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Analysis
by VulDB Data Team • 08/12/2022
The vulnerability described in CVE-2022-2503 resides within the Linux kernel's device-mapper subsystem and specifically impacts the LoadPin security mechanism designed to protect against unauthorized kernel module and firmware loading. Dm-verity serves as a foundational component for establishing a trusted root of trust for filesystems, ensuring that data cannot be tampered with without detection. LoadPin extends this protection by restricting module and firmware loading operations to only those originating from the trusted root filesystem, thereby preventing malicious code from being loaded through compromised peripheral devices or untrusted storage paths. This security model relies on the integrity of device-mapper table operations, which are critical for maintaining the kernel's security boundaries.
The technical flaw manifests in the device-mapper table reload functionality where privileged users can exploit a loophole to replace active dm-table targets with equivalent dm-linear targets. This manipulation occurs during runtime without requiring a system reboot, effectively bypassing the LoadPin restrictions that were designed to prevent such unauthorized operations. The vulnerability stems from insufficient validation during device-mapper table reloads, allowing an attacker with root privileges to modify the underlying storage mapping while maintaining the appearance of legitimate operations. This bypass mechanism directly undermines the security model by enabling the loading of untrusted kernel modules and firmware that would otherwise be rejected by the LoadPin enforcement mechanisms.
The operational impact of this vulnerability is severe and potentially catastrophic for systems relying on LoadPin for security protection. An attacker with root access can leverage this vulnerability to execute arbitrary kernel code, effectively achieving complete system compromise and persistence. This capability extends to peripheral devices that do not independently verify firmware updates, creating a vector for long-term system infiltration. The vulnerability essentially nullifies the security guarantees provided by LoadPin, allowing malicious actors to load kernel modules that can manipulate system behavior, establish backdoors, or exfiltrate sensitive data. The implications extend beyond immediate exploitation to include potential privilege escalation across multiple system components that depend on the integrity of the kernel module loading process.
The recommended mitigation involves upgrading to a kernel version that includes the fix referenced in commit 4caae58406f8ceb741603eee460d79bacca9b1b5, which addresses the device-mapper table reload validation issue. This fix ensures that table reload operations properly validate target types and prevent substitution with equivalent but untrusted mappings. Organizations should also consider implementing additional security controls such as kernel lockdown modes, module signing enforcement, and monitoring for unauthorized device-mapper table modifications. The vulnerability aligns with CWE-284 Access Control Issues and represents a significant concern within the ATT&CK framework under privilege escalation and defense evasion techniques. System administrators must ensure that all affected systems are updated promptly and that appropriate monitoring is implemented to detect potential exploitation attempts, as the vulnerability can be leveraged to establish persistent access to compromised systems without requiring additional attack vectors.