CVE-2025-71072: Linux Kernel Privilege Escalation Flaw

CVE-2025-71072 Overview

A vulnerability has been identified in the Linux kernel's shared memory (shmem) subsystem where improper error recovery during rename operations can lead to system instability. The issue occurs when maple_tree insertions fail under low-memory conditions, causing simple_offset_rename() and simple_offset_rename_exchange() functions to not recover properly from these failures.

Critical Impact
Systems under memory pressure performing shmem rename operations may experience inconsistent filesystem state, potentially leading to data corruption or denial of service conditions.

Affected Products

Linux Kernel (shmem subsystem)
Systems utilizing shared memory filesystem operations
Linux distributions running affected kernel versions

Discovery Timeline

2026-01-13 - CVE CVE-2025-71072 published to NVD
2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-71072

Vulnerability Analysis

This vulnerability exists in the Linux kernel's shmem (shared memory) implementation, specifically affecting rename operations within the filesystem. The core issue stems from inadequate error handling when maple_tree data structure insertions fail due to severe memory pressure.

The simple_offset_rename() function does not properly recover when maple_tree insertions fail, leaving the filesystem in an inconsistent state. Similarly, simple_offset_rename_exchange() suffers from the same recovery deficiency. A critical dependency exists in shmem_whiteout(), which expects that upon successful completion, the caller will proceed to d_move(). This expectation means shmem_rename2() must not fail after a successful shmem_whiteout() call.

The root cause involves the atomicity and ordering of operations during rename handling, where failures mid-operation cannot be gracefully reversed without special consideration for the maple_tree's behavior characteristics.

Root Cause

The vulnerability originates from insufficient error handling logic in the shmem rename path. When the system experiences severe memory shortages, mtree_store() operations can fail. The existing code did not account for these failure scenarios, leading to incomplete or corrupted rename operations.

The fix leverages a key property of mtree_store(): it cannot fail if the index being stored is already present in the tree as a singleton. For simple_offset_rename_exchange(), careful operation ordering resolves the issue. For simple_offset_rename(), a preinsertion of the target into the new directory's tree prevents failures. This preinsertion must occur in shmem_rename2() rather than simple_offset_rename() itself to avoid failures after a successful shmem_whiteout() call.

Attack Vector

This vulnerability can be triggered under specific conditions:

The attack vector requires an adversary to create memory pressure conditions on a target system while shmem rename operations are being performed. An attacker with local access could potentially:

Exhaust system memory through legitimate or malicious resource allocation
Trigger shmem rename operations during the memory-constrained state
Cause the system to enter an inconsistent state due to failed error recovery

While exploitation requires local access and specific timing conditions, successful exploitation could result in filesystem inconsistencies, potential data loss, or denial of service conditions.

Detection Methods for CVE-2025-71072

Indicators of Compromise

Unexpected filesystem errors or inconsistencies in tmpfs/shmem mounted directories
Kernel log messages indicating maple_tree insertion failures during rename operations
System instability or kernel panics during low-memory conditions with active shmem operations

Detection Strategies

Monitor kernel logs for shmem-related error messages, particularly those mentioning simple_offset_rename or mtree_store failures
Implement memory pressure monitoring to detect potential exploitation attempts during high-memory conditions
Deploy file integrity monitoring on critical shmem-backed directories to detect unexpected state changes

Monitoring Recommendations

Configure alerting for out-of-memory conditions coinciding with shmem filesystem activity
Enable kernel debugging options to capture detailed error information during rename failures
Monitor system memory utilization patterns and investigate anomalous consumption spikes

How to Mitigate CVE-2025-71072

Immediate Actions Required

Update to a patched Linux kernel version containing the fix commits
Monitor systems for memory pressure conditions that could trigger the vulnerability
Consider temporarily reducing shmem usage on critical systems until patches are applied

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix implements proper error recovery by leveraging maple_tree properties and reordering operations to prevent failures after critical points in the rename process.

Relevant kernel commits addressing this issue:

Workarounds

Ensure adequate system memory is available to reduce the likelihood of memory allocation failures
Limit the use of shmem-based filesystems on memory-constrained systems
Implement memory resource controls (cgroups) to prevent resource exhaustion attacks

bash

# Monitor shmem usage and memory pressure
cat /proc/meminfo | grep -E "Shmem|MemFree|MemAvailable"

# Check kernel version for patch status
uname -r

# Review kernel logs for related errors
dmesg | grep -i "shmem\|rename\|maple"