CVE-2025-39765
📋 TL;DR
A NULL pointer dereference vulnerability in the Linux kernel's ALSA timer subsystem where ida_free() is called on an unallocated ID when kasprintf() fails during timer creation. This affects Linux systems with ALSA sound subsystem enabled, potentially causing kernel panics or system instability.
💻 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 system crash and denial of service, requiring physical or remote reboot.
Likely Case
System instability or crash when specific ALSA timer operations fail due to memory allocation issues.
If Mitigated
Warning message in kernel logs without system crash if kernel is configured with proper error handling.
🎯 Exploit Status
Requires ability to trigger ALSA timer creation with specific conditions causing kasprintf() to fail. Discovered via syzkaller fuzzing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing commits 34327b362ce2849a5eb02f47e800049e7a20a0ba, 5003a65790ed66be882d1987cc2ca86af0de3db1, or af386b52531d14c4b20f11c452787b1b6dd4eb8d
Vendor Advisory: https://git.kernel.org/stable/c/34327b362ce2849a5eb02f47e800049e7a20a0ba
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 ALSA timer module
LinuxPrevent loading of the vulnerable ALSA timer module
echo 'blacklist snd-timer' >> /etc/modprobe.d/blacklist.conf
rmmod snd-timer
🧯 If You Can't Patch
- Restrict user access to ALSA device nodes (/dev/snd/timer*)
- Monitor kernel logs for 'ida_free called for id=0 which is not allocated' warnings
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if it contains the fix commits. Run: uname -r and compare with distribution security advisories.Check Version:
uname -rVerify Fix Applied:
Verify kernel version after update and check that warning messages no longer appear in dmesg when testing ALSA timer operations.📡 Detection & Monitoring
Log Indicators:
- Kernel log messages containing 'ida_free called for id=0 which is not allocated'
- System crash/panic logs related to ALSA timer
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND "ida_free called for id=0"