CVE-2022-3565: Linux Kernel Use-After-Free Vulnerability

CVE-2022-3565 Overview

A critical use-after-free vulnerability has been discovered in the Linux Kernel affecting the del_timer function within the file drivers/isdn/mISDN/l1oip_core.c of the Bluetooth component. This memory corruption flaw allows an attacker with local access to potentially execute arbitrary code, compromise system integrity, and cause denial of service conditions on affected Linux systems.

Critical Impact

This use-after-free vulnerability in the Linux Kernel's mISDN/Bluetooth subsystem enables local attackers to potentially gain elevated privileges, execute arbitrary code, or crash the system by exploiting improper memory handling during timer deletion operations.

Affected Products

• Linux Kernel (multiple versions affected)
• Debian-based Linux distributions
• Linux systems utilizing the mISDN/Bluetooth driver

Discovery Timeline

• 2022-10-17 - CVE-2022-3565 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-3565

Vulnerability Analysis

This vulnerability represents a classic use-after-free memory corruption issue in the Linux Kernel's ISDN mISDN layer, specifically within the Layer 1 over IP (l1oip) core functionality. The vulnerable code path involves the del_timer function, which is responsible for managing timer objects in the kernel.

Use-after-free vulnerabilities occur when a program continues to reference memory after it has been freed, leading to undefined behavior. In this case, the improper synchronization of timer deletion operations allows for a race condition where memory can be accessed after being released back to the kernel allocator. An attacker who can trigger this condition could potentially corrupt kernel memory, leading to privilege escalation or arbitrary code execution in kernel context.

The vulnerability requires local access to the system, but does not require elevated privileges to trigger. Once exploited, an attacker could achieve complete compromise of the affected system's confidentiality, integrity, and availability.

Root Cause

The root cause of this vulnerability lies in improper memory management within the del_timer function in drivers/isdn/mISDN/l1oip_core.c. The code fails to properly synchronize timer deletion operations, creating a window where freed memory can still be referenced. This is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) and CWE-662 (Improper Synchronization), indicating both memory safety and concurrency issues contribute to the vulnerability.

Attack Vector

The attack vector for CVE-2022-3565 requires local access to the vulnerable Linux system. An attacker with an unprivileged local account could craft specific inputs to trigger the race condition in the timer deletion code path. By carefully timing their operations, the attacker can cause the kernel to reference freed memory, potentially overwriting it with controlled data before the dangling reference is used.

The vulnerability manifests in the timer management code within the mISDN Bluetooth driver subsystem. When the del_timer function is called, improper synchronization allows for a timing window where the timer structure may be freed while still being referenced elsewhere in the code. Exploitation requires understanding the kernel's memory allocation patterns and timing the attack to control the contents of the freed memory region. For detailed technical analysis, see the Linux Bluetooth Commit Update that addresses this issue.

Detection Methods for CVE-2022-3565

Indicators of Compromise

• Unexpected kernel panics or system crashes related to the mISDN or Bluetooth subsystems
• Suspicious local user activity attempting to interact with ISDN/Bluetooth driver interfaces
• Kernel oops messages referencing l1oip_core.c or related timer functions
• Memory corruption artifacts in kernel logs indicating use-after-free conditions

Detection Strategies

• Monitor kernel logs (dmesg) for use-after-free warnings or memory corruption messages related to mISDN components
• Deploy kernel-level memory sanitizers (KASAN) in test environments to detect exploitation attempts
• Implement system call auditing to track interactions with the affected driver interfaces
• Use intrusion detection systems to monitor for known exploitation patterns targeting kernel timer vulnerabilities

Monitoring Recommendations

• Enable comprehensive kernel logging with particular attention to memory allocation failures and timer-related operations
• Configure alerts for kernel oops or panic events, especially those mentioning the Bluetooth or ISDN subsystems
• Monitor for unusual local privilege escalation attempts following kernel instability
• Implement endpoint detection and response (EDR) solutions capable of detecting kernel-level exploitation attempts

How to Mitigate CVE-2022-3565

Immediate Actions Required

• Update Linux Kernel to the latest patched version from your distribution's security repository
• Review Debian LTS Security Announcement for distribution-specific guidance
• Restrict local access to systems running vulnerable kernel versions until patches can be applied
• Disable the mISDN Bluetooth driver module if not required for system functionality

Patch Information

The Linux Kernel development team has released a security patch to address this vulnerability. The fix is available in the bluetooth-next git repository with commit ID 2568a7e0832ee30b0a351016d03062ab4e0e0a3f. The patch properly synchronizes timer deletion operations to prevent the use-after-free condition. Users should update to patched kernel versions through their distribution's package manager or apply the patch directly from the Linux Bluetooth Commit Update.

Workarounds

• Blacklist the mISDN_core and l1oip kernel modules if ISDN over IP functionality is not required
• Implement strict access controls to limit local user access on vulnerable systems
• Use kernel live patching solutions (kpatch, livepatch) if available for your distribution to apply fixes without rebooting
• Employ mandatory access control (SELinux, AppArmor) policies to restrict access to the vulnerable driver interfaces

# Configuration example - Disable vulnerable mISDN modules
# Add to /etc/modprobe.d/blacklist-misdn.conf
blacklist mISDN_core
blacklist l1oip

# Prevent automatic loading
echo "install mISDN_core /bin/true" >> /etc/modprobe.d/blacklist-misdn.conf
echo "install l1oip /bin/true" >> /etc/modprobe.d/blacklist-misdn.conf

# Unload modules if currently loaded (requires reboot if in use)
modprobe -r l1oip
modprobe -r mISDN_core