CVE-2026-68107 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu/vcn4: avoid rereading IB param length
Reuse the parameter length returned by vcn_v4_0_enc_find_ib_param() instead of rereading it from the IB.
This avoids a potential TOCTOU issue if the IB contents change between reads.
(cherry picked from commit dbb02b4755f8c1f3773263f2d779872c1c0c073a)
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/10/2026
The vulnerability in question affects the Linux kernel's amdgpu driver, specifically within the vcn4 hardware video codec implementation. This issue resides in the direct rendering manager subsystem where the driver handles video encoding operations through the Video Codec Unit version 4. The flaw manifests when processing instruction buffers for video encoding tasks, creating a potential race condition that could compromise system integrity and security.
The technical root cause involves a Time-of-Check to Time-of-Use vulnerability pattern where the driver performs redundant reads of instruction buffer parameters. When the vcn_v4_0_enc_find_ib_param() function is called to locate encoding parameters within an instruction buffer, it returns a specific parameter length value. However, the subsequent code would reread this same information from the instruction buffer without utilizing the previously obtained length value, creating an opportunity for inconsistent data retrieval.
This TOCTOU vulnerability occurs because the instruction buffer contents may change between the initial parameter discovery operation and the subsequent re-reading of the same data. If an attacker can manipulate or modify the instruction buffer content during this brief window, they could potentially exploit the discrepancy between the two reads to execute unauthorized operations or bypass security checks. The vulnerability specifically impacts the video encoding functionality of AMD graphics hardware through the vcn4 codec implementation.
The operational impact of this vulnerability extends beyond simple data inconsistency issues. When exploited, this race condition could allow malicious actors to manipulate video encoding parameters, potentially leading to unauthorized code execution within kernel space or bypassing access controls for video processing operations. The vulnerability affects systems utilizing AMD graphics hardware with vcn4 codec support, particularly those running recent Linux kernel versions where the problematic code path exists.
Security mitigations for this issue involve implementing proper parameter caching mechanisms and ensuring that once a value is read from a potentially volatile data source, subsequent references use the cached value rather than performing redundant reads. The fix addresses the vulnerability by reusing the parameter length value returned by the vcn_v4_0_enc_find_ib_param() function instead of performing additional reads from the instruction buffer. This approach eliminates the race condition window and ensures consistent parameter handling throughout the encoding process.
This vulnerability aligns with CWE-367, which specifically addresses Time-of-Check to Time-of-Use flaws in security contexts. The remediation strategy follows established best practices for preventing TOCTOU issues by reducing the number of data access points and ensuring consistent data usage patterns. The fix also demonstrates adherence to kernel security principles where redundant operations that could introduce race conditions are eliminated through proper code design and parameter handling.
The implementation of this patch reflects standard ATT&CK techniques for kernel-level privilege escalation through data manipulation vulnerabilities. By addressing the root cause at the instruction buffer processing level, the fix prevents potential exploitation vectors that could lead to unauthorized system access or privilege escalation within the graphics subsystem. Security teams should prioritize applying this kernel update across systems utilizing AMD graphics hardware with vcn4 codec support to prevent potential exploitation of this race condition vulnerability.