CVE-2023-53645
📋 TL;DR
This CVE-2023-53645 is a use-after-free vulnerability in the Linux kernel's BPF subsystem where bpf_refcount_acquire could increment a zero refcount on freed memory when called on non-owning references after certain operations fail. This affects systems running vulnerable Linux kernel versions with BPF programs that use refcount operations. Attackers could potentially exploit this to cause kernel crashes or achieve local privilege escalation.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to system crash, or potential local privilege escalation allowing attackers to gain root access on the affected system.
Likely Case
Kernel crash or system instability when BPF programs trigger the specific failure path, resulting in denial of service.
If Mitigated
No impact if the vulnerable code path is not executed by BPF programs or if proper kernel hardening is in place.
🎯 Exploit Status
Exploitation requires ability to load BPF programs, which typically requires CAP_BPF or root privileges on most systems.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in kernel commits 7793fc3babe9fea908e57f7c187ea819f9fd7e95 and d906d1b940b9dbf0a3e821d6b32a51c369273d91
Vendor Advisory: https://git.kernel.org/stable/c/7793fc3babe9fea908e57f7c187ea819f9fd7e95
Restart Required: Yes
Instructions:
1. Update to a kernel version containing the fix. 2. Check your distribution's security advisories for specific patched kernel versions. 3. Reboot the system after kernel update.
🔧 Temporary Workarounds
Disable BPF subsystem
linuxDisable the BPF subsystem to prevent loading of BPF programs that could trigger the vulnerability
echo 1 > /proc/sys/kernel/unprivileged_bpf_disabled
sysctl -w kernel.unprivileged_bpf_disabled=1
Restrict BPF program loading
linuxUse capabilities or SELinux/AppArmor to restrict which users can load BPF programs
setcap -r /usr/bin/bpftool
Use appropriate SELinux/AppArmor policies
🧯 If You Can't Patch
- Implement strict access controls to prevent unauthorized users from loading BPF programs
- Monitor for suspicious BPF program loading and kernel warning messages related to refcount operations
🔍 How to Verify
Check if Vulnerable:
Check kernel version and verify if BPF refcount operations are used in your environment. Look for kernel warning messages containing 'refcount_t: addition on 0; use-after-free' in dmesg or system logs.Check Version:
uname -rVerify Fix Applied:
Verify kernel version is updated to a version containing the fix commits. Check that bpf_refcount_acquire properly handles NULL returns for non-owning references in BPF programs.📡 Detection & Monitoring
Log Indicators:
- Kernel warning messages containing 'refcount_t: addition on 0; use-after-free'
- BPF program loading events from unauthorized users
- System crashes or kernel panics
Network Indicators:
- Not applicable - this is a local kernel vulnerability
SIEM Query:
source="kernel" AND "refcount_t: addition on 0; use-after-free" OR source="audit" AND "BPF" AND "prog_load"