CVE-2021-47299
📋 TL;DR
This is a use-after-free vulnerability in the Linux kernel's XDP (eXpress Data Path) subsystem that occurs during BPF link cleanup. It allows local attackers to cause kernel memory corruption, potentially leading to system crashes or privilege escalation. Systems running affected Linux kernel versions with XDP/BPF functionality enabled are vulnerable.
💻 Affected Systems
- Linux Kernel
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to denial of service, or potential privilege escalation to root if an attacker can control the freed memory region.
Likely Case
Kernel crash/panic causing system instability and denial of service, requiring reboot.
If Mitigated
Limited to denial of service if kernel hardening features like KASAN or KPTI are enabled.
🎯 Exploit Status
Exploitation requires local access and knowledge of XDP/BPF subsystem. The race condition timing makes reliable exploitation challenging.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in kernel commits: 5acc7d3e8d342858405fbbc671221f676b547ce7, a7537dc73e69ad9c0b67ad24ad3ebee954ed0af6, ca9ba1de8f09976b45ccc8e655c51c6201992139
Vendor Advisory: https://git.kernel.org/stable/c/5acc7d3e8d342858405fbbc671221f676b547ce7
Restart Required: Yes
Instructions:
1. Update to a kernel version containing the fix commits. 2. Check your distribution's security advisories for backported patches. 3. Reboot the system after kernel update.
🔧 Temporary Workarounds
Disable XDP/BPF functionality
linuxPrevent use of XDP and BPF features that trigger the vulnerable code path
echo 0 > /proc/sys/net/core/bpf_jit_enable
Remove XDP programs from network interfaces
🧯 If You Can't Patch
- Restrict local user access to systems with XDP/BPF functionality
- Implement kernel hardening features like KASAN to detect and mitigate exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check kernel version: uname -r. If running kernel 5.13 or earlier, check if XDP/BPF is enabled via /proc/sys/net/core/bpf_jit_enableCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits: grep -q '5acc7d3e8d342858405fbbc671221f676b547ce7\|a7537dc73e69ad9c0b67ad24ad3ebee954ed0af6\|ca9ba1de8f09976b45ccc8e655c51c6201992139' /proc/version_signature📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages mentioning 'use-after-free'
- KASAN reports for bpf_xdp_link_release
- System crash/reboot logs
Network Indicators:
- Unusual XDP program loading/unloading patterns
SIEM Query:
source="kernel" AND ("use-after-free" OR "bpf_xdp_link_release" OR "KASAN: bad access")🔗 References
- https://git.kernel.org/stable/c/5acc7d3e8d342858405fbbc671221f676b547ce7
- https://git.kernel.org/stable/c/a7537dc73e69ad9c0b67ad24ad3ebee954ed0af6
- https://git.kernel.org/stable/c/ca9ba1de8f09976b45ccc8e655c51c6201992139
- https://git.kernel.org/stable/c/5acc7d3e8d342858405fbbc671221f676b547ce7
- https://git.kernel.org/stable/c/a7537dc73e69ad9c0b67ad24ad3ebee954ed0af6
- https://git.kernel.org/stable/c/ca9ba1de8f09976b45ccc8e655c51c6201992139
