CVE-2021-47258 – This CVE describes a memory leak vulnerability ... (How to Fix)

Q: What is the severity of CVE-2021-47258?

CVE-2021-47258 has a CVSS score of 5.5 (MEDIUM). This CVE describes a memory leak vulnerability in the Linux kernel's SCSI subsystem. When scsi_host_alloc() fails during device initialization, improper cleanup leads to kernel memory leaks. This affects all Linux systems using SCSI storage devices.

📋 TL;DR

This CVE describes a memory leak vulnerability in the Linux kernel's SCSI subsystem. When scsi_host_alloc() fails during device initialization, improper cleanup leads to kernel memory leaks. This affects all Linux systems using SCSI storage devices.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE description, but patches exist for multiple stable branches

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects systems using SCSI storage devices where scsi_host_alloc() can fail during initialization.

📦 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 →

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

Sustained exploitation could cause kernel memory exhaustion leading to system instability, crashes, or denial of service.

🟠

Likely Case

Gradual memory consumption over time causing performance degradation, particularly on systems with frequent SCSI device initialization failures.

🟢

If Mitigated

With proper patching, no impact beyond normal system operation.

🌐 Internet-Facing: LOW - Requires local access or ability to trigger SCSI device initialization failures.

🏢 Internal Only: MEDIUM - Could be exploited by local users or through other vulnerabilities to degrade system performance.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires ability to trigger SCSI device initialization failures, typically requiring local access or specific conditions.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Multiple stable kernel versions with commits: 2dc85045ae65b9302a1d2e2ddd7ce4c030153a6a, 45d83db4728127944b237c0c8248987df9d478e7, 66a834d092930cf41d809c0e989b13cd6f9ca006, 79296e292d67fa7b5fb8d8c27343683e823872c8, 7a696ce1d5d16a33a6cd6400bbcc0339b2460e11

Vendor Advisory: https://git.kernel.org/stable/c/2dc85045ae65b9302a1d2e2ddd7ce4c030153a6a

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.

🔧 Temporary Workarounds

Disable SCSI device hotplug

linux

Prevent new SCSI devices from being initialized to avoid triggering the vulnerable code path

echo 'blacklist scsi_mod' > /etc/modprobe.d/disable-scsi.conf
update-initramfs -u

🧯 If You Can't Patch

Monitor system memory usage for unusual increases
Restrict local user access to prevent potential exploitation

🔍 How to Verify

Check if Vulnerable:

Check kernel version and compare with patched versions from kernel git repository

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version includes one of the fix commits: 2dc85045ae65b9302a1d2e2ddd7ce4c030153a6a or related patches

📡 Detection & Monitoring

Log Indicators:

Kernel oom-killer messages
System memory exhaustion warnings
SCSI device initialization failures in dmesg

Network Indicators:

None - local vulnerability only

SIEM Query:

source="kernel" AND ("Out of memory" OR "oom-killer" OR "SCSI" AND "failed")

📊 Metadata

CVE ID: CVE-2021-47258

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-401

Published: May 21, 2024

Last Updated: April 30, 2025

🔗 References

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