CVE-2023-52903 – A race condition vulnerability in the Linux ker... (How to Fix)

Q: What is the severity of CVE-2023-52903?

CVE-2023-52903 has a CVSS score of 5.5 (MEDIUM). A race condition vulnerability in the Linux kernel's io_uring subsystem for IOPOLL operations can cause a kernel warning and potential denial of service. This affects Linux systems using io_uring with IOPOLL enabled, particularly when combined with SQPOLL. The issue occurs during overflow handling when multiple threads access completion queue resources without proper locking.

📋 TL;DR

A race condition vulnerability in the Linux kernel's io_uring subsystem for IOPOLL operations can cause a kernel warning and potential denial of service. This affects Linux systems using io_uring with IOPOLL enabled, particularly when combined with SQPOLL. The issue occurs during overflow handling when multiple threads access completion queue resources without proper locking.

💻 Affected Systems

Products:

Linux Kernel

Versions: Kernel versions before the fix commits (specific versions vary by distribution)

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when io_uring with IOPOLL is enabled and actively used. The vulnerability is more complex when IOPOLL is combined with SQPOLL.

📦 What is this software?

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 →

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 →

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 →

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 →

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 →

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

Kernel panic or system crash leading to complete denial of service, requiring system reboot.

🟠

Likely Case

Kernel warning messages in system logs and temporary disruption of io_uring operations until the system recovers.

🟢

If Mitigated

Minor performance impact with proper kernel patching and monitoring.

🌐 Internet-Facing: LOW - Requires local access or ability to execute code on the system.

🏢 Internal Only: MEDIUM - Could be exploited by malicious local users or through compromised applications to cause system instability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and ability to trigger specific io_uring operations. The vulnerability was discovered through syzbot fuzzing.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in kernel commits: 544d163d659d45a206d8929370d5a2984e546cb7, 7fc3990dad04a677606337ebc61964094d6cb41b, de77faee280163ff03b7ab64af6c9d779a43d4c4, ed4629d1e968359fbb91d0a3780b1e86a2c08845

Vendor Advisory: https://git.kernel.org/stable/c/544d163d659d45a206d8929370d5a2984e546cb7

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix commits. 2. Check your distribution's security advisories for specific patched kernel versions. 3. Reboot the system after kernel update.

🔧 Temporary Workarounds

Disable io_uring IOPOLL

linux

Disable IOPOLL feature in io_uring to prevent triggering the vulnerability

echo 0 > /proc/sys/fs/io_uring/poll

Disable io_uring entirely

linux

Completely disable io_uring subsystem if not required

modprobe -r io_uring
echo 'blacklist io_uring' > /etc/modprobe.d/blacklist-io_uring.conf

🧯 If You Can't Patch

Implement strict access controls to limit local user privileges
Monitor system logs for io_uring warning messages and implement alerting

🔍 How to Verify

Check if Vulnerable:

Check kernel version and if io_uring IOPOLL is enabled: cat /proc/sys/fs/io_uring/poll

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version contains the fix commits and check dmesg for absence of io_uring overflow warnings

📡 Detection & Monitoring

Log Indicators:

Kernel warning messages containing 'io_cqring_event_overflow' or 'io_uring' in dmesg or /var/log/kern.log

Network Indicators:

None - this is a local kernel vulnerability

SIEM Query:

source="kernel" AND ("io_cqring_event_overflow" OR "io_uring" AND "WARNING")

📊 Metadata

CVE ID: CVE-2023-52903

CVSS v3 Score: 5.5 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-667

Published: August 21, 2024

Last Updated: September 13, 2024

🔗 References

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🔗 Related Vulnerabilities

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