CVE-2026-68206 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
media: v4l2-ctrls: validate HEVC active reference counts
HEVC slice parameters are shared stateless V4L2 controls, but the common validation path does not verify the active L0/L1 reference counts before driver-specific code consumes them.
The original report came from Cedrus, but the active count bounds are not Cedrus-specific. Validate them in the common HEVC slice control path so stateless HEVC drivers get the same basic guarantees as soon as the control is queued.
Do not reject ref_idx_l0/ref_idx_l1 entries here. Existing userspace may use out-of-range sentinel values such as 0xff for missing references, and some hardware can use that information for concealment. Keep this common check limited to the active reference counts.
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Analysis
by VulDB Data Team • 08/11/2026
The vulnerability resides in the linux kernel's v4l2 video4linux2 controls implementation specifically within the HEVC (High Efficiency Video Coding) slice parameter handling mechanism. This represents a validation gap where shared stateless V4L2 controls for HEVC slice parameters lack proper bounds checking on active reference counts before driver-specific code processes them. The issue affects the common validation path that handles HEVC slice controls, creating a potential security risk through improper input validation of reference count parameters.
The technical flaw manifests in the absence of validation for active L0/L1 reference counts within the shared HEVC slice control processing pathway. While the kernel's V4L2 subsystem properly manages various video control parameters, the specific validation for active reference counts occurs too late in the processing chain, after driver-specific code has already consumed these values. This timing issue creates a window where malformed or out-of-bounds reference count values could lead to unpredictable behavior or potential exploitation scenarios within hardware drivers that process HEVC video streams.
This vulnerability impacts stateless HEVC drivers across multiple hardware implementations by removing the basic validation guarantees that should be applied universally when HEVC slice controls are queued. The security implications extend beyond the original Cedrus-specific report since the active count bounds validation is not limited to a single hardware vendor but affects all stateless HEVC drivers that rely on the common V4L2 control infrastructure. The vulnerability aligns with CWE-129 Input Validation and CWE-787 Out-of-bounds Write categories, as improper reference count validation could lead to buffer overflows or memory corruption issues.
The operational impact of this vulnerability is significant for video processing systems that utilize stateless HEVC decoding capabilities. When userspace applications submit HEVC slice controls with malformed reference counts, the kernel's validation occurs too late in the processing pipeline, potentially allowing hardware drivers to process invalid data without proper bounds checking. This could result in system instability, unexpected behavior during video decoding, or in worst-case scenarios, potential privilege escalation or denial of service conditions.
The mitigation strategy involves implementing validation of active reference counts within the common HEVC slice control path rather than deferring this check to driver-specific code. This approach ensures that all stateless HEVC drivers receive consistent basic guarantees when processing HEVC controls. The solution maintains backward compatibility by preserving existing userspace behavior where sentinel values like 0xff are used for missing references, which hardware may utilize for concealment purposes. This validation approach aligns with ATT&CK technique T1068 Exploitation for Privilege Escalation and follows the principle of least privilege by ensuring proper input sanitization before processing.
The fix addresses the fundamental issue of delayed validation in kernel subsystems while maintaining existing functionality for hardware-specific features that depend on sentinel values. By moving the reference count validation to the common control path, the kernel ensures consistent security posture across all HEVC implementations without breaking existing userspace compatibility. This approach follows established security practices for preventing out-of-bounds operations and aligns with defensive programming principles where input validation occurs as early as possible in the processing pipeline, reducing the attack surface for potential exploitation scenarios.