CVE-2023-26605 Overview
CVE-2023-26605 is a use-after-free vulnerability in the Linux kernel version 6.0.8. The flaw resides in the inode_cgwb_move_to_attached function within fs/fs-writeback.c and relates to __list_del_entry_valid. Local attackers with low privileges can trigger memory corruption that may lead to privilege escalation or kernel-level code execution. The weakness is classified under CWE-416 (Use After Free) and affects systems running the impacted kernel build.
Critical Impact
A local attacker can exploit the use-after-free condition in the filesystem writeback path to corrupt kernel memory, potentially achieving privilege escalation, denial of service, or arbitrary kernel code execution.
Affected Products
- Linux Kernel 6.0.8
- Linux distributions shipping the affected kernel build
- NetApp products referenced in advisory NTAP-20230316-0010
Discovery Timeline
- 2023-02-26 - CVE-2023-26605 published to the National Vulnerability Database (NVD)
- 2025-05-05 - Last updated in NVD database
Technical Details for CVE-2023-26605
Vulnerability Analysis
The vulnerability exists in the cgroup writeback (cgwb) tracking logic of the Linux kernel filesystem writeback subsystem. The function inode_cgwb_move_to_attached in fs/fs-writeback.c manipulates inode list entries that have already been freed. When the kernel later accesses these dangling list pointers through __list_del_entry_valid, it operates on memory that may have been reallocated for other kernel objects.
The issue is reachable through filesystem operations that interact with the cgroup writeback machinery. An attacker holding local access with low privileges can trigger the conditions that cause the kernel to dereference freed memory. Successful exploitation undermines memory integrity in kernel space and provides a primitive for further attacks.
Root Cause
The root cause is improper lifecycle management of inode list entries within the cgroup writeback move operation. The code path fails to ensure that list entries remain valid before performing list manipulation, allowing a freed object to be referenced. This results in a use-after-free condition where __list_del_entry_valid validates and processes pointers that no longer reference live kernel objects.
Attack Vector
Exploitation requires local access with low privileges and no user interaction. An attacker triggers specific filesystem and cgroup writeback operations to reach the vulnerable code path in inode_cgwb_move_to_attached. Controlling the freed memory region through heap spraying or related kernel heap manipulation techniques enables an attacker to influence kernel state. The result can be privilege escalation to root, kernel memory disclosure, or system crash.
No verified public proof-of-concept code is available. Technical details are documented in the upstream fix commit 4e3c51f4e805 and the LKML discussion thread.
Detection Methods for CVE-2023-26605
Indicators of Compromise
- Unexpected kernel oops or panic messages referencing inode_cgwb_move_to_attached or __list_del_entry_valid in dmesg or /var/log/kern.log
- KASAN (Kernel Address Sanitizer) reports flagging use-after-free in fs/fs-writeback.c
- Anomalous process privilege transitions from unprivileged users to root without legitimate setuid execution
- Unexplained system instability or crashes during heavy filesystem writeback activity on cgroup-managed workloads
Detection Strategies
- Enable KASAN on test kernels matching production builds to surface use-after-free conditions during workload replay
- Audit installed kernel versions across the fleet and flag any host running Linux kernel 6.0.8 without the upstream fix
- Monitor kernel ring buffer output for list corruption warnings, which often precede successful exploitation attempts
Monitoring Recommendations
- Centralize kernel logs and alert on signatures matching list_del corruption, BUG: KASAN, or stack traces involving writeback functions
- Track unexpected privilege escalations and new root-owned processes spawned from user sessions
- Correlate kernel crash dumps with user activity to identify reproducible exploitation patterns
How to Mitigate CVE-2023-26605
Immediate Actions Required
- Upgrade the Linux kernel to a version that includes upstream commit 4e3c51f4e805
- Apply distribution-provided kernel updates from your Linux vendor as soon as they are available
- For NetApp environments, review and apply guidance from NetApp Security Advisory NTAP-20230316-0010
- Restrict local shell access on multi-tenant systems until patched kernels are deployed
Patch Information
The vulnerability is resolved by upstream kernel commit 4e3c51f4e805291b057d12f5dda5aeb50a538dc4, which corrects the inode list handling in inode_cgwb_move_to_attached. Linux distribution maintainers backported the fix into supported stable kernel branches. Administrators should verify their running kernel includes the patch by checking the kernel changelog or commit history before declaring remediation complete.
Workarounds
- Reduce attack surface by limiting local user access to trusted accounts only
- Disable cgroup v2 writeback features where operationally feasible until patching is complete
- Apply mandatory access controls such as SELinux or AppArmor profiles that constrain unprivileged user filesystem operations
# Verify the installed kernel version and confirm the patch is present
uname -r
# On Debian/Ubuntu systems, update the kernel
sudo apt update && sudo apt install --only-upgrade linux-image-generic
# On RHEL/CentOS/Fedora systems, update the kernel
sudo dnf update kernel
# Reboot to load the patched kernel
sudo reboot
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
