CVE-2021-47305 – This CVE describes a memory leak vulnerability ... (How to Fix)

Q: What is the severity of CVE-2021-47305?

CVE-2021-47305 has a CVSS score of 5.5 (MEDIUM). This CVE describes a memory leak vulnerability in the Linux kernel's dma-buf/sync_file subsystem. When fence merging fails, the kernel doesn't properly release allocated fence objects, leading to gradual memory exhaustion. This affects any system using the affected Linux kernel versions with DMA buffer operations.

📋 TL;DR

This CVE describes a memory leak vulnerability in the Linux kernel's dma-buf/sync_file subsystem. When fence merging fails, the kernel doesn't properly release allocated fence objects, leading to gradual memory exhaustion. This affects any system using the affected Linux kernel versions with DMA buffer operations.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE description, but patches are available in stable kernel trees

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Vulnerability requires DMA buffer operations to be triggered. Not all systems may use the affected code paths.

📦 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

Sustained exploitation could lead to kernel memory exhaustion, causing system instability, denial of service, or potential kernel crashes.

🟠

Likely Case

Gradual memory leak over time leading to performance degradation and eventual system instability requiring reboot.

🟢

If Mitigated

Minimal impact with proper memory monitoring and regular system maintenance.

🌐 Internet-Facing: LOW - Requires local access or ability to trigger specific kernel operations.

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

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires ability to trigger specific kernel operations, typically through local access or compromised applications.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Patches available in stable kernel trees (see references for specific commits)

Vendor Advisory: https://git.kernel.org/stable/c/0d514185ae792d3a1903c8e1a83899aa996705ce

Restart Required: Yes

Instructions:

1. Identify current kernel version. 2. Update to patched kernel version from your distribution's repositories. 3. Reboot system to load new kernel.

🔧 Temporary Workarounds

Limit DMA buffer operations

linux

Restrict applications that use DMA buffer operations if not essential

🧯 If You Can't Patch

Implement strict memory monitoring and alerting for unusual memory consumption
Restrict local user access and application privileges to minimize attack surface

🔍 How to Verify

Check if Vulnerable:

Check kernel version and compare against patched versions in distribution advisories

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version after update matches patched version and monitor for memory leaks

📡 Detection & Monitoring

Log Indicators:

Kernel oops messages
Out of memory errors in system logs
Increasing memory usage without clear cause

SIEM Query:

source="kernel" AND ("out of memory" OR "kernel panic" OR memory_usage > threshold)

📊 Metadata

CVE ID: CVE-2021-47305

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-617

Published: May 21, 2024

Last Updated: May 12, 2025

🔗 References

📤 Share & Export

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🔗 Related Vulnerabilities

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