CVE-2025-38263
📋 TL;DR
A NULL pointer dereference vulnerability in the Linux kernel's bcache subsystem allows local attackers to cause a kernel panic (denial of service) by triggering memory allocation failures during cache set registration. This affects systems using the bcache device mapper for caching block devices. Attackers need local access to the system.
💻 Affected Systems
- Linux kernel with bcache support
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to system crash and denial of service, potentially causing data corruption or loss if bcache is handling critical storage.
Likely Case
Local denial of service through kernel panic when bcache operations fail due to memory constraints.
If Mitigated
Minimal impact if bcache is not used or memory allocation failures are prevented through resource limits.
🎯 Exploit Status
Requires local access and ability to trigger memory allocation failures in bcache operations. Not trivial but feasible for local attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with commits 1e46ed947ec658f89f1a910d880cd05e42d3763e, 1f25f2d3fa29325320c19a30abf787e0bd5fc91b, 3f9e128186c99a117e304f1dce6d0b9e50c63cd8, 553f560e0a74a7008ad9dba05c3fd05da296befb, or 667c3f52373ff5354cb3543e27237eb7df7b2333
Vendor Advisory: https://git.kernel.org/stable/c/1e46ed947ec658f89f1a910d880cd05e42d3763e
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel. 3. Verify bcache functionality if used.
🔧 Temporary Workarounds
Disable bcache module
linuxPrevent loading of bcache kernel module if not needed
echo 'install bcache /bin/false' >> /etc/modprobe.d/disable-bcache.conf
rmmod bcache
Blacklist bcache module
linuxBlacklist bcache module to prevent automatic loading
echo 'blacklist bcache' >> /etc/modprobe.d/blacklist-bcache.conf
🧯 If You Can't Patch
- Avoid using bcache for storage caching
- Implement strict memory limits to reduce chance of allocation failures triggering the bug
🔍 How to Verify
Check if Vulnerable:
Check if bcache module is loaded: lsmod | grep bcache. If loaded, check kernel version against patched versions.Check Version:
uname -rVerify Fix Applied:
Verify kernel version includes one of the fix commits. Check dmesg for bcache-related NULL pointer dereference errors.📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages mentioning cache_set_flush
- NULL pointer dereference at 00000000000009f8 in bcache logs
- bcache register_cache() error messages
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND ("cache_set_flush" OR "bcache" AND "NULL pointer")🔗 References
- https://git.kernel.org/stable/c/1e46ed947ec658f89f1a910d880cd05e42d3763e
- https://git.kernel.org/stable/c/1f25f2d3fa29325320c19a30abf787e0bd5fc91b
- https://git.kernel.org/stable/c/3f9e128186c99a117e304f1dce6d0b9e50c63cd8
- https://git.kernel.org/stable/c/553f560e0a74a7008ad9dba05c3fd05da296befb
- https://git.kernel.org/stable/c/667c3f52373ff5354cb3543e27237eb7df7b2333
- https://git.kernel.org/stable/c/c4f5e7e417034b05f5d2f5fa9a872db897da69bd
- https://git.kernel.org/stable/c/d54681938b777488e5dfb781b566d16adad991de
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
