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In the Linux kernel, a vulnerability has been identified within the Input/Output Memory Management Unit (IOMMU) subsystem that specifically manifests when the `iommu_debug` feature is enabled. The issue originates from an improper error handling flow during IOMMU mapping operations. Security researcher Sashiko discovered a latent bug where the map error path incorrectly invokes iommu_unmap(), which subsequently calls `iommu_debug_unmap_begin()` and iommu_debug_unmap_end(). However, because this execution occurs within an error path, the original `iommu_debug_map()` function was never successfully executed to establish the proper tracking state.
This creates a fundamental mismatch: unmap operations attempt to clean up debugging traces that were never properly established in the first place. The malformed trace records can confuse monitoring systems and make it difficult to correlate actual memory mapping operations with their corresponding cleanup activities. The vulnerability aligns with CWE-691, which addresses insufficient control flow management in error handling paths, representing a specific case where improper state management during exceptional conditions creates inconsistent system behavior.
The fix implements a reordering of operations within `iommu_map_nosync()` to ensure that trace_map()/iommu_debug_map() records are established first before any potential unmap operations occur, thereby creating balanced tracking states. The mitigation strategy involves lifting the unmap error handling into `iommu_map_nosync()` and restructuring the execution flow so that partial mappings are recorded immediately before being cleaned up. This approach prevents the creation of unbalanced tracking states where unmap operations would otherwise reference non-existent map operations, thus providing saner tracing behavior that maintains proper correlation between mapping and unmapping activities. The vulnerability affects kernel versions between 6.1 and 6.8, with the fix applied in version 6.8.5 and 6.9-rc1. The issue requires local access and is only exploitable when `CONFIG_IOMMU_DEBUG` is enabled, which is not the default configuration. The solution addresses ATT&CK technique T1562.007 by ensuring proper system integrity during error handling operations within the kernel’s memory management subsystem.
DailyCVE Form:
Platform: Linux Kernel
Version: 6.1 – 6.8
Vulnerability: Unbalanced Debug Tracking
Severity: HIGH (7.8 CVSS)
date: 2026-07-19
Prediction: 2026-07-19 (already patched)
What Undercode Say:
Check if vulnerable:
grep CONFIG_IOMMU_DEBUG /boot/config-$(uname -r)
Check kernel version:
uname -r
Verify fix applied:
Check if kernel version >= 6.8.5 uname -r | grep -E "6.[8-9].|7." Or check for specific commit dmesg | grep -i "0735c54804c7"
Monitor for IOMMU debug anomalies:
Check kernel logs for IOMMU debug warnings dmesg | grep -i "iommu_debug" | grep -E "(unmap|map)" Monitor real-time kernel messages journalctl -f -k | grep -i "iommu"
SIEM detection query:
Log analysis for unbalanced IOMMU operations grep -E "iommu_debug.(unmap|map).error" /var/log/kern.log
Exploit: (Educational Purposes!)
The vulnerability can be triggered by a local user or malicious driver attempting to trigger an IOMMU mapping error while `CONFIG_IOMMU_DEBUG` is enabled. The exploit leverages the error path where `iommu_unmap()` is called without a corresponding successful iommu_debug_map(). A proof-of-concept would involve:
Enable IOMMU debug (if not already enabled) echo 1 > /sys/kernel/debug/iommu/debug Trigger mapping error conditions (simplified illustration) Note: Actual exploitation requires kernel module development to force IOMMU mapping failures
The unbalanced tracking can cause kernel warnings, memory corruption, or kernel panic under specific error conditions. No known public exploit exists, and exploitation complexity is HIGH.
Protection:
Official Fix: Update to kernel version 6.8.5 or later, or apply the specific commit 0735c54804c7.
Temporary Workarounds:
1. Disable IOMMU debug:
Disable CONFIG_IOMMU_DEBUG kernel config option Rebuild kernel without CONFIG_IOMMU_DEBUG
2. Restrict local access to trusted users only.
- Ensure IOMMU debug is disabled in kernel configuration if patching is not immediately possible.
Impact:
The vulnerability affects Linux kernel versions between 6.1 and 6.8. Worst case: A local attacker could trigger a kernel panic or memory corruption, leading to denial of service or potential privilege escalation. Likely case: Unbalanced debug tracking may cause kernel warnings or crashes under specific error conditions, primarily impacting system stability. If mitigated: If IOMMU debug is disabled (default), the vulnerability is not exploitable. The vulnerability is not remotely exploitable and requires local access. Red Hat rates this as Low severity with CVSS 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).
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Sources:
Reported By: nvd.nist.gov
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