CVE-2021-47505
📋 TL;DR
This Linux kernel vulnerability allows use-after-free attacks when using asynchronous I/O (aio) polling with signalfd or binder file descriptors. Attackers could potentially crash the system or execute arbitrary code with kernel privileges. Systems running Linux kernel versions 4.18 through affected patched versions 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 →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 privilege escalation leading to full system compromise, arbitrary code execution, or persistent rootkits.
Likely Case
Kernel panic or system crash causing denial of service.
If Mitigated
Limited impact if proper kernel hardening and privilege separation are implemented.
🎯 Exploit Status
Exploitation requires local access and specific conditions (aio polling with signalfd/binder). No public exploits known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patched in kernel commits: 321fba81ec034f88aea4898993c1bf15605c023f, 4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f, 47ffefd88abfffe8a040bcc1dd0554d4ea6f7689, 50252e4b5e989ce64555c7aef7516bdefc2fea72, 60d311f9e6381d779d7d53371f87285698ecee24
Vendor Advisory: https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution vendor. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.
🔧 Temporary Workarounds
Disable aio polling
linuxPrevent use of aio polling which triggers the vulnerability
echo 0 > /proc/sys/fs/aio-max-nr
sysctl -w fs.aio-max-nr=0
Restrict signalfd and binder usage
linuxLimit access to signalfd and binder file descriptors
chmod 600 /dev/binder
setfacl -m u:root:rw /dev/binder
🧯 If You Can't Patch
- Implement strict access controls to limit who can use aio, signalfd, and binder functionality
- Monitor system logs for crash reports or unusual kernel behavior
🔍 How to Verify
Check if Vulnerable:
Check kernel version: uname -r and compare with affected versions (4.18+). Check if aio polling is enabled.Check Version:
uname -rVerify Fix Applied:
Verify kernel version after update and ensure it includes the patched commits. Check dmesg for any related errors.📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- Use-after-free warnings in dmesg
- System crashes related to aio or polling
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND ("use-after-free" OR "aio" OR "POLLFREE" OR "panic")🔗 References
- https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f
- https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f
- https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689
- https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72
- https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24
- https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f
- https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f
- https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689
- https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72
- https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24
