CVE-2026-31391 Overview
A memory leak vulnerability has been identified in the Linux kernel's atmel-sha204a cryptographic driver. The vulnerability occurs when memory allocation fails during transformation operations, but the ->tfm_count reference counter is not properly decremented. This can lead to resource exhaustion and denial of service conditions by blocking future read operations on the affected device.
Critical Impact
Improper reference counter management in the atmel-sha204a crypto driver can block future device reads when memory allocation fails, potentially leading to denial of service.
Affected Products
- Linux kernel with atmel-sha204a crypto driver enabled
- Systems using Atmel SHA204A hardware security modules
- Embedded devices utilizing the atmel-sha204a interface
Discovery Timeline
- April 03, 2026 - CVE CVE-2026-31391 published to NVD
- April 07, 2026 - Last updated in NVD database
Technical Details for CVE-2026-31391
Vulnerability Analysis
The vulnerability resides in the atmel-sha204a cryptographic driver within the Linux kernel's crypto subsystem. When a transformation context (tfm) is allocated, the driver increments a reference counter (->tfm_count) to track active transformations. However, when memory allocation fails during this process, the error handling path fails to decrement the counter before returning.
This oversight creates a resource leak where the tfm_count remains incremented despite no actual resource being allocated. Over time, or through deliberate exploitation, this can cause the counter to reach its maximum value, effectively blocking all future read operations on the cryptographic device since the driver checks this counter before allowing new transformations.
Root Cause
The root cause is improper error handling in the memory allocation path of the atmel-sha204a driver. When kmalloc() or similar allocation functions return NULL due to out-of-memory (OOM) conditions, the driver correctly returns an error code but fails to undo the reference counter increment that occurred earlier in the allocation sequence. This violates the principle of atomic operation cleanup where all state changes should be rolled back upon failure.
Attack Vector
An attacker with local access to the system could potentially trigger this vulnerability by:
- Causing repeated memory pressure situations on the system
- Initiating multiple cryptographic operations that stress the atmel-sha204a driver
- Exploiting the OOM condition handling to leak reference counts
- Eventually exhausting the reference counter, blocking legitimate cryptographic operations
The vulnerability requires local access to trigger memory allocation failures and interact with the crypto subsystem. While not directly exploitable for code execution, it presents a denial of service risk for systems relying on the Atmel SHA204A hardware security module for cryptographic operations.
The fix involves adding a decrement operation (->tfm_count--) in the error handling path to ensure the reference counter remains consistent when memory allocation fails. Multiple kernel commits have been issued across different stable branches to address this issue. For technical implementation details, refer to the kernel commit 1ab70c2.
Detection Methods for CVE-2026-31391
Indicators of Compromise
- Unusual memory pressure or OOM killer activity targeting processes using crypto operations
- Increasing tfm_count values in the atmel-sha204a driver without corresponding active transformations
- Failed read operations on /dev/atmel_sha204a or related device nodes
- System logs showing repeated allocation failures in the crypto subsystem
Detection Strategies
- Monitor kernel logs (dmesg) for OOM conditions specifically mentioning the crypto or atmel-sha204a subsystem
- Track system memory usage patterns and correlate with cryptographic operation failures
- Implement watchdog monitoring for cryptographic device availability
Monitoring Recommendations
- Enable kernel tracing for the crypto subsystem to detect anomalous tfm allocation patterns
- Set up alerts for persistent cryptographic device read failures
- Monitor /proc/meminfo and cgroup memory statistics for unusual allocation patterns during crypto operations
- Review SentinelOne Singularity platform alerts for kernel-level anomalies on affected systems
How to Mitigate CVE-2026-31391
Immediate Actions Required
- Update the Linux kernel to a patched version containing the fix
- Review systems using Atmel SHA204A hardware security modules for potential impact
- Monitor affected systems for signs of resource exhaustion or blocked crypto operations
- Consider temporarily disabling the atmel-sha204a driver if not critical to operations until patched
Patch Information
The Linux kernel development team has released patches across multiple stable branches to address this vulnerability. The fix ensures proper decrement of the ->tfm_count reference counter when memory allocation fails, preventing resource leaks.
Available patches:
- Kernel Commit 1ab70c2
- Kernel Commit 2bfc83c
- Kernel Commit 66ee9c1
- Kernel Commit 6f50204
- Kernel Commit d240b07
- Kernel Commit fd262dc
Workarounds
- Ensure adequate system memory is available to reduce OOM conditions
- Implement memory cgroup limits to prevent runaway processes from causing system-wide OOM
- If the atmel-sha204a driver is not required, disable or blacklist the kernel module
- Apply rate limiting on cryptographic operations to reduce allocation pressure
# Blacklist the atmel-sha204a module if not required
echo "blacklist atmel-sha204a" >> /etc/modprobe.d/blacklist-atmel.conf
# Verify the module is not loaded
lsmod | grep atmel
# Force unload if currently loaded (use with caution)
modprobe -r atmel-sha204a
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
