CVE-2025-71131: Linux Kernel Use-After-Free Vulnerability

CVE-2025-71131 Overview

A use-after-free vulnerability has been identified in the Linux kernel's cryptographic subsystem, specifically within the seqiv (sequence IV) module. The vulnerability occurs when the req->iv pointer is dereferenced after calling crypto_aead_encrypt, at which point the underlying request may have already been freed by an asynchronous completion handler.

Critical Impact

This vulnerability could lead to memory corruption, information disclosure, or potential code execution in systems utilizing the affected cryptographic operations with AEAD (Authenticated Encryption with Associated Data) algorithms.

Affected Products

• Linux kernel (multiple versions with seqiv module)
• Systems using AEAD cryptographic operations
• Servers and embedded devices running affected kernel versions

Discovery Timeline

• 2026-01-14 - CVE CVE-2025-71131 published to NVD
• 2026-01-19 - Last updated in NVD database

Technical Details for CVE-2025-71131

Vulnerability Analysis

The vulnerability exists in the Linux kernel's seqiv cryptographic module, which handles sequence number-based initialization vectors for AEAD algorithms. When crypto_aead_encrypt is called, the cryptographic operation may complete asynchronously. In this scenario, the completion callback can free the request structure before the calling function returns.

The problematic code pattern involves checking req->iv against info after the encryption call has returned. Since the request may have been freed by an asynchronous completion handler, this dereference accesses potentially freed memory, resulting in a classic use-after-free condition.

The fix introduces a new local variable unaligned_info to preserve the necessary information before the encryption call, eliminating the need to access the potentially freed request structure afterward.

Root Cause

The root cause is a race condition in the asynchronous cryptographic operation handling. The seqiv module fails to account for the fact that AEAD encryption operations can complete asynchronously, meaning the request structure and its associated iv field may be deallocated by the completion handler before the initiating function finishes execution. This represents a classic use-after-free pattern where a pointer is dereferenced after the memory it references has been freed.

Attack Vector

While the attack vector is currently unknown due to limited severity information, exploitation would likely require:

1. An attacker with the ability to trigger cryptographic operations using the seqiv module
2. Specific timing conditions to win the race condition between the asynchronous completion and the subsequent req->iv access
3. Local access to the system or the ability to influence cryptographic operations remotely through a network service

The vulnerability could potentially be triggered through network services that utilize AEAD encryption with sequence IV generation, though exploitation complexity may be high due to the timing-dependent nature of the bug.

Detection Methods for CVE-2025-71131

Indicators of Compromise

• Kernel crash logs (oops/panic) referencing the seqiv or crypto subsystem
• Memory corruption errors in dmesg related to AEAD operations
• Unexpected system instability when cryptographic operations are performed
• KASAN (Kernel Address Sanitizer) reports showing use-after-free in crypto code paths

Detection Strategies

• Monitor kernel logs for memory access violations in the crypto subsystem
• Enable KASAN in development/testing environments to detect use-after-free conditions
• Deploy kernel crash monitoring to identify seqiv-related failures
• Use SentinelOne's kernel-level behavioral detection to identify anomalous memory access patterns

Monitoring Recommendations

• Enable comprehensive kernel logging for the crypto subsystem
• Implement SIEM rules to alert on kernel crash events mentioning seqiv or crypto_aead
• Monitor system stability metrics for systems performing heavy cryptographic workloads
• Review audit logs for unusual cryptographic operation patterns

How to Mitigate CVE-2025-71131

Immediate Actions Required

• Update to a patched Linux kernel version containing the fix
• Review and apply patches from the kernel git repository
• Evaluate workloads to identify systems with heavy AEAD cryptographic usage
• Consider temporarily reducing reliance on affected cryptographic operations if patches cannot be immediately applied

Patch Information

Multiple patches have been released across stable kernel branches. The fix introduces a new variable unaligned_info to store the necessary information before calling crypto_aead_encrypt, preventing access to the potentially freed req->iv field.

Relevant kernel commits are available at:

• Kernel Git Commit 0279978
• Kernel Git Commit 1820253
• Kernel Git Commit 50f196d
• Kernel Git Commit 50fdb78
• Kernel Git Commit 5476f7f
• Kernel Git Commit baf0e2d
• Kernel Git Commit ccbb964

Workarounds

• No direct workarounds are available for this vulnerability
• If patching is not immediately possible, consider limiting access to cryptographic operations to trusted processes
• Monitor systems closely for signs of exploitation while awaiting patch deployment
• Consider using alternative cryptographic algorithms that do not rely on the seqiv module if available

# Check current kernel version
uname -r

# Verify if seqiv module is loaded
lsmod | grep seqiv

# Check kernel logs for related errors
dmesg | grep -i "seqiv\|crypto\|aead"