CVE-2021-47427 – This CVE describes a use-after-free vulnerabili... (How to Fix)

Q: What is the severity of CVE-2021-47427?

CVE-2021-47427 has a CVSS score of 7.8 (HIGH). This CVE describes a use-after-free vulnerability in the Linux kernel's iSCSI subsystem. An attacker could potentially exploit this to cause kernel memory corruption, leading to system crashes or arbitrary code execution with kernel privileges. Systems running affected Linux kernel versions with iSCSI functionality enabled are vulnerable.

📋 TL;DR

This CVE describes a use-after-free vulnerability in the Linux kernel's iSCSI subsystem. An attacker could potentially exploit this to cause kernel memory corruption, leading to system crashes or arbitrary code execution with kernel privileges. Systems running affected Linux kernel versions with iSCSI functionality enabled are vulnerable.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific kernel versions between the vulnerable commit d39df158518c and the fix commits. Check stable kernel trees for exact affected versions.

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if iSCSI subsystem is enabled and in use. Many systems may not have iSCSI configured.

📦 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel panic leading to denial of service, or potential privilege escalation to kernel level allowing complete system compromise.

🟠

Likely Case

System instability, kernel crashes, or denial of service affecting iSCSI storage operations.

🟢

If Mitigated

Limited impact if iSCSI is not used or systems are properly segmented.

🌐 Internet-Facing: LOW - iSCSI typically operates on internal networks, not directly internet-exposed.

🏢 Internal Only: MEDIUM - Requires access to iSCSI services, which are typically internal but could be exploited by malicious insiders or compromised internal systems.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: HIGH

Exploitation requires triggering specific iSCSI abort handling scenarios. No public exploits known as of knowledge cutoff.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits 1642f51ac0d4f2b55d5748094c49ff8f7191b93c or 258aad75c62146453d03028a44f2f1590d58e1f6

Vendor Advisory: https://git.kernel.org/stable/c/1642f51ac0d4f2b55d5748094c49ff8f7191b93c

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution. 2. For custom kernels, apply the fix commits to your kernel source. 3. Recompile and install the kernel. 4. Reboot the system.

🔧 Temporary Workarounds

Disable iSCSI

linux

If iSCSI functionality is not required, disable the iSCSI kernel module

modprobe -r iscsi_tcp
modprobe -r libiscsi
modprobe -r scsi_transport_iscsi
echo 'blacklist iscsi_tcp' >> /etc/modprobe.d/blacklist.conf
echo 'blacklist libiscsi' >> /etc/modprobe.d/blacklist.conf
echo 'blacklist scsi_transport_iscsi' >> /etc/modprobe.d/blacklist.conf

🧯 If You Can't Patch

Restrict network access to iSCSI services using firewall rules
Monitor systems for abnormal iSCSI activity or kernel crashes

🔍 How to Verify

Check if Vulnerable:

Check kernel version and verify if iSCSI modules are loaded: 'lsmod | grep -i iscsi' and 'uname -r'

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is patched and iSCSI modules are either disabled or system is stable after applying patches

📡 Detection & Monitoring

Log Indicators:

Kernel oops messages in /var/log/kern.log or dmesg
Unexpected system crashes or reboots
Abnormal iSCSI connection terminations

Network Indicators:

Unusual iSCSI traffic patterns or connection attempts

SIEM Query:

source="kernel" AND ("Oops" OR "panic" OR "BUG") AND ("iscsi" OR "SCSI")

📊 Metadata

CVE ID: CVE-2021-47427

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-416

Published: May 21, 2024

Last Updated: December 31, 2024

🔗 References

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🔗 Related Vulnerabilities

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