CVE-2021-40490
📋 TL;DR
A race condition vulnerability in the ext4 filesystem's inline data handling in Linux kernel versions up to 5.13.13 allows local attackers to corrupt filesystem metadata or cause denial of service. This affects systems using ext4 with inline data enabled, primarily Linux servers and workstations. Attackers need local access to exploit this vulnerability.
💻 Affected Systems
- Linux kernel
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Filesystem corruption leading to data loss, system crashes, or potential privilege escalation if combined with other vulnerabilities.
Likely Case
System instability, kernel panics, or denial of service through filesystem corruption.
If Mitigated
Minimal impact with proper access controls limiting local user privileges.
🎯 Exploit Status
Race conditions are difficult to exploit reliably and require precise timing. No public exploits have been documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel 5.13.14 and later
Vendor Advisory: https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git/commit/?id=9e445093e523f3277081314c864f708fd4bd34aa
Restart Required: Yes
Instructions:
1. Update Linux kernel to version 5.13.14 or later. 2. For distributions: Use package manager (apt, yum, dnf) to update kernel package. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable ext4 inline data feature
linuxMount ext4 filesystems without inline data support to prevent exploitation
mount -o remount,noinline_data /mount/point
🧯 If You Can't Patch
- Restrict local user access and implement least privilege principles
- Monitor system logs for filesystem corruption or kernel panic events
🔍 How to Verify
Check if Vulnerable:
Check kernel version: uname -r. If version is 5.13.13 or earlier and ext4 with inline data is used, system is vulnerable.Check Version:
uname -rVerify Fix Applied:
Verify kernel version is 5.13.14 or later: uname -r📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- ext4 filesystem error messages in dmesg or /var/log/kern.log
- Unexpected system reboots
Network Indicators:
- None - local exploit only
SIEM Query:
source="kernel" AND ("panic" OR "ext4 error" OR "filesystem corruption")🔗 References
- https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git/commit/?id=9e445093e523f3277081314c864f708fd4bd34aa
- https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html
- https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/M6VS2DLGT7TK7URKAS2KWJL3S533SGVA/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XJGX3DMJT6MRBW2XEF3TWVHYWZW3DG3N/
- https://security.netapp.com/advisory/ntap-20211004-0001/
- https://www.debian.org/security/2021/dsa-4978
- https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git/commit/?id=9e445093e523f3277081314c864f708fd4bd34aa
- https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html
- https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/M6VS2DLGT7TK7URKAS2KWJL3S533SGVA/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XJGX3DMJT6MRBW2XEF3TWVHYWZW3DG3N/
- https://security.netapp.com/advisory/ntap-20211004-0001/
- https://www.debian.org/security/2021/dsa-4978
