CVE-2026-31514: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-31514 Overview

A vulnerability has been identified in the Linux kernel's EROFS (Enhanced Read-Only File System) implementation affecting file-backed mount operations. The flaw exists in the handling of IO requests processed by vfs_iocb_iter_read(), where interruption by SIGKILL can result in a short read condition that incorrectly marks unused folios in the bio as uptodate.

When a read operation is interrupted during filemap_read, the function returns only the number of bytes actually copied. However, the erofs_fileio_ki_complete function subsequently marks all folios in the bio as uptodate, including those that were never actually read. This creates a data integrity issue where applications may receive stale or uninitialized memory contents believing them to be valid file data.

Critical Impact

Data integrity issues in EROFS file-backed mounts where interrupted reads may cause unread folios to be incorrectly marked as valid, potentially exposing uninitialized memory contents to applications.

Affected Products

• Linux Kernel (EROFS filesystem component)
• Systems using EROFS with file-backed mount configurations
• Linux distributions with affected kernel versions

Discovery Timeline

• April 22, 2026 - CVE CVE-2026-31514 published to NVD
• April 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-31514

Vulnerability Analysis

This vulnerability is categorized as an Input Validation Error within the Linux kernel's EROFS filesystem implementation. The root cause lies in the improper handling of short read conditions when IO operations are interrupted by signals.

In the vulnerable code path, when a SIGKILL signal is sent to a process during a read operation, vfs_iocb_iter_read() returns the number of bytes successfully copied rather than completing the full read. The issue manifests because erofs_fileio_ki_complete does not properly account for partial reads and marks all folios in the bio structure as uptodate, regardless of whether they actually contain valid data.

The call stack demonstrates the issue clearly:

1. vfs_read initiates the read operation
2. filemap_read processes the read through filemap_get_pages
3. filemap_readahead triggers erofs_fileio_readahead
4. erofs_fileio_rq_submit calls vfs_iocb_iter_read
5. A signal is detected in filemap_get_pages, causing a short read
6. erofs_fileio_ki_complete incorrectly marks all folios as uptodate

This can lead to applications receiving data from folios that were never populated with actual file contents, potentially exposing uninitialized kernel memory or causing data corruption in userspace applications.

Root Cause

The root cause is the failure to properly propagate error conditions when vfs_iocb_iter_read() returns a short read due to signal interruption. The completion handler erofs_fileio_ki_complete unconditionally marks all folios as uptodate without verifying how many bytes were actually transferred.

Attack Vector

The attack vector for this vulnerability is primarily local. An attacker with the ability to execute code on the system could potentially exploit this by:

1. Mounting an EROFS filesystem with a file backend
2. Initiating read operations on the filesystem
3. Sending SIGKILL signals to interrupt reads at strategic points
4. Observing potentially uninitialized memory contents returned as valid file data

While direct exploitation for privilege escalation is limited, the vulnerability could be leveraged for information disclosure in certain scenarios where kernel memory contents are exposed to unprivileged processes.

Detection Methods for CVE-2026-31514

Indicators of Compromise

• Unexpected data corruption or inconsistencies when reading from EROFS file-backed mounts
• Application crashes due to invalid data read from EROFS filesystems
• Unusual SIGKILL signals targeting processes performing EROFS read operations
• Kernel log messages related to EROFS read errors or bio completion anomalies

Detection Strategies

• Monitor for systems using EROFS with file-backed mount configurations
• Implement file integrity monitoring on EROFS-mounted content to detect data inconsistencies
• Review system logs for EROFS-related error messages or warnings
• Track kernel versions deployed against known vulnerable versions

Monitoring Recommendations

• Enable kernel auditing for EROFS filesystem operations
• Monitor for unusual signal activity (SIGKILL) during filesystem operations
• Deploy SentinelOne Singularity Platform for real-time kernel-level threat detection
• Implement alerting for EROFS mount operations on production systems

How to Mitigate CVE-2026-31514

Immediate Actions Required

• Update to patched Linux kernel versions containing the fix
• Review systems for EROFS file-backed mount usage and assess exposure
• Consider temporarily avoiding EROFS file-backed mounts on critical systems until patches are applied
• Monitor kernel commit logs for stable branch backports

Patch Information

The vulnerability has been resolved by setting short read bio with an error directly, ensuring that folios which were not successfully read are not incorrectly marked as uptodate. Multiple patches have been released across kernel stable branches:

• Kernel Commit 5a5f23ef5431639db1ac3a0b274aef3a84cc413c
• Kernel Commit 5cf3972c8221abdb1b464a14ccf8103d840b9085
• Kernel Commit d1ba7d6b3cd1757b108d7b6856c92ae661d6c323
• Kernel Commit eade54040384f54b7fb330e4b0975c5734850b3c

Workarounds

• Avoid using EROFS with file-backed mount configurations until patches are applied
• Use alternative filesystem types for scenarios requiring file-backed mounts
• Implement application-level data validation for critical reads from EROFS filesystems
• Restrict signal delivery permissions to reduce the ability to trigger the vulnerable code path

# Check if EROFS with file-backed mount is in use
mount | grep erofs

# Check current kernel version
uname -r

# Verify if EROFS module is loaded
lsmod | grep erofs