CVE-2026-68400 Overview
CVE-2026-68400 is a Linux kernel vulnerability in the arm_ffa firmware driver. The flaw resides in how the driver calculates the offset of the Endpoint Memory Access Descriptor array within a memory region descriptor. Instead of using the descriptor's ep_mem_offset field as required by the Arm Firmware Framework for Arm (FF-A) specification, the driver defaults to sizeof(struct ffa_mem_region). This mismatch can cause the driver to read structures from an incorrect memory offset, producing out-of-bounds reads and unpredictable memory access when handling FF-A memory-sharing operations.
Critical Impact
A local, authenticated attacker interacting with the FF-A interface can trigger out-of-bounds memory access in the kernel, impacting confidentiality, integrity, and availability on affected Arm systems.
Affected Products
- Linux kernel versions containing the pre-patch arm_ffa firmware driver
- Arm platforms using the Firmware Framework for Arm (FF-A) memory-sharing interface
- Distributions shipping vulnerable stable kernels prior to commits 8ef18f0, b39b08e, and b4d9613
Discovery Timeline
- 2026-08-10 - CVE-2026-68400 published to NVD
- 2026-08-13 - Last updated in NVD database
Technical Details for CVE-2026-68400
Vulnerability Analysis
The arm_ffa driver implements the Arm Firmware Framework for Arm (FF-A) memory-sharing protocol. FF-A memory transactions use a memory region descriptor (struct ffa_mem_region) followed by an array of Endpoint Memory Access Descriptors that identify which endpoints receive access. The FF-A specification requires consumers to locate this array using the ep_mem_offset field embedded in the descriptor.
The vulnerable driver ignores ep_mem_offset and instead assumes the array begins immediately after sizeof(struct ffa_mem_region). When firmware provides a descriptor with a non-default offset, the driver reads endpoint records from the wrong memory location. The fix also reorders ffa_mem_region_additional_setup() earlier in the setup flow and adds sanity checks so the calculated descriptor offsets do not exceed max_fragsize [CWE-125].
Root Cause
The root cause is an incorrect offset calculation. The driver used a hardcoded structure-size assumption instead of the specification-defined ep_mem_offset value. Missing bounds validation against max_fragsize allowed calculated offsets to reference memory outside the descriptor fragment, resulting in out-of-bounds reads and potential state corruption.
Attack Vector
Exploitation requires local access with low privileges on an Arm system that exposes the FF-A interface. An attacker capable of influencing FF-A memory-sharing descriptors, or a compromised low-privileged component interacting with the driver, can craft descriptors that steer the kernel into invalid memory reads. Successful exploitation can leak sensitive kernel memory, corrupt driver state, or crash the kernel.
No verified public exploit code is available. See the Kernel Commit 8ef18f0 Security Fix for the corrective patch details.
Detection Methods for CVE-2026-68400
Indicators of Compromise
- Kernel oops or panic messages referencing arm_ffa, ffa_mem_region, or endpoint descriptor parsing routines
- Unexpected FF-A transaction failures logged by firmware or the kernel firmware/arm_ffa subsystem
- Repeated crashes on Arm platforms coinciding with workloads that invoke FF-A memory-sharing calls
Detection Strategies
- Inventory running kernels on Arm hosts and compare against fixed stable kernel commits 8ef18f0, b39b08e, and b4d9613
- Monitor dmesg and journal logs for anomalies in the arm_ffa driver and correlate with process activity invoking FF-A operations
- Enable kernel address sanitizer (KASAN) in test environments to surface out-of-bounds reads in the FF-A parsing path
Monitoring Recommendations
- Forward kernel logs to a central telemetry pipeline and alert on arm_ffa error patterns or repeated OOPS events
- Track invocation of FF-A syscalls or firmware calls from unprivileged processes as unusual behavior
- Baseline expected FF-A activity on production Arm hosts to identify anomalous descriptor traffic
How to Mitigate CVE-2026-68400
Immediate Actions Required
- Apply the upstream Linux kernel patches referenced by commits 8ef18f0, b39b08e, and b4d9613 on all Arm hosts using the arm_ffa driver
- Rebuild or update distribution kernels to versions incorporating these commits and reboot affected systems
- Restrict local access on Arm platforms exposing FF-A until patches are deployed
Patch Information
The fix uses ep_mem_offset from the descriptor to locate the endpoint memory access array, moves ffa_mem_region_additional_setup() earlier in the setup flow, and adds sanity checks against max_fragsize. Reference the Kernel Commit b39b08e Security Update and Kernel Commit b4d9613 Vulnerability Patch for the full diffs.
Workarounds
- Where feasible, disable or unload the arm_ffa driver on systems that do not require FF-A memory sharing
- Limit local shell and container access on Arm hosts to trusted users until the patched kernel is deployed
- Constrain workloads that interact with FF-A to sandboxed environments while patching is pending
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
