CVE-2026-64057 Overview
CVE-2026-64057 is a Linux kernel vulnerability in the Andrew File System (AFS) implementation. The flaw resides in the afs_get_link() function, which handles symbolic link resolution. The AFS filesystem fails to perform correct locking around symlink operations, creating multiple race condition scenarios. These include unsynchronized calls to afs_read_single(), missing RCU (Read-Copy-Update) barriers during pathwalks, and race conditions when a third party updates symlink contents on the server.
The vulnerability requires local access with low privileges and can result in memory leaks, use-after-free conditions, or inconsistent symlink resolution. Exploitation can lead to kernel memory corruption or information disclosure on systems mounting AFS volumes.
Critical Impact
Local attackers with low privileges can trigger race conditions in the Linux kernel AFS symlink handler, potentially causing memory corruption, information leaks, or denial of service on affected systems.
Affected Products
- Linux kernel with AFS filesystem support enabled
- Systems mounting AFS volumes via the in-kernel AFS client
- Stable Linux kernel branches prior to the patches referenced in commits 77ea917 and c0410ad
Discovery Timeline
- 2026-07-19 - CVE-2026-64057 published to NVD
- 2026-07-20 - Last updated in NVD database
Technical Details for CVE-2026-64057
Vulnerability Analysis
The vulnerability affects the AFS kernel client's symbolic link handling logic. Three distinct concurrency defects converge in the afs_get_link() code path. First, the function performs no locking around afs_read_single(), allowing concurrent ->get_link() invocations to race and leak allocated buffers. Second, the code accesses buffer pointers during RCU pathwalk without appropriate RCU barriers, violating memory-ordering guarantees required for lock-free readers. Third, the symlink contents can be modified by a remote party on the AFS server while local threads are reading them, producing inconsistent or corrupted results.
The upstream fix moves symlink handling into a dedicated file and introduces the validate_lock around afs_read_single(). A separate copy of the symlink contents is maintained with an rcu_head and a reference count for non-RCU pathwalks. The read and write-to-cache routines are split from the directory equivalents, and I/O buffers are discarded promptly after use to reduce memory footprint.
Root Cause
The root cause is a combination of Race Condition and improper RCU synchronization [CWE-362, CWE-416]. The AFS symlink code reused directory-oriented I/O paths without adding the locking primitives required for the symlink lifecycle. Buffer pointers accessed during RCU pathwalk lacked rcu_dereference() semantics, and no reference counting protected the symlink buffer from concurrent reclaim.
Attack Vector
Exploitation requires local access to a system with AFS volumes mounted. An unprivileged local user triggers concurrent readlink() or path-resolution operations against an AFS symlink while the same symlink is being refreshed from the server. The resulting race can free or overwrite buffer memory that another thread is still reading, leading to kernel memory corruption or disclosure of freed slab contents.
No public proof-of-concept exploit is available. Technical details are described in the upstream kernel patches referenced in the Kernel Git Commit 77ea917 and Kernel Git Commit c0410ad.
Detection Methods for CVE-2026-64057
Indicators of Compromise
- Kernel oops or panic messages referencing afs_get_link, afs_read_single, or symlink pathwalk functions in dmesg output
- KASAN (Kernel Address Sanitizer) reports of use-after-free or slab-out-of-bounds on AFS-related allocations
- Unexpected EIO or truncated readlink() results on AFS-mounted paths under concurrent access
Detection Strategies
- Inventory hosts with the kafs kernel module loaded using lsmod | grep kafs and correlate against running kernel version
- Compare running kernel versions against distribution advisories referencing commits 77ea917 and c0410ad
- Enable kernel lockdep and KASAN in test environments to surface remaining AFS locking issues during regression testing
Monitoring Recommendations
- Forward kernel logs to a centralized logging or SIEM platform and alert on AFS subsystem stack traces
- Monitor mount events for AFS filesystems and correlate with elevated readlink() syscall rates from unprivileged users
- Track kernel package versions across the fleet and flag hosts still running vulnerable builds
How to Mitigate CVE-2026-64057
Immediate Actions Required
- Apply the upstream Linux kernel patches referenced by commits 77ea917cbed62882a33114b1e23ededb977e4287 and c0410adf3da6db46f3513411fcf95e63c2f1d1ad
- Update to the fixed stable kernel release provided by your Linux distribution and reboot affected hosts
- Restrict local shell access on systems mounting AFS volumes to trusted users until patching is complete
Patch Information
The fix is available in the mainline Linux kernel through the two referenced stable commits. The patches relocate symlink handling to a dedicated source file, introduce validate_lock around afs_read_single(), add RCU-safe reference counting for symlink buffers, and separate symlink read paths from directory read paths. Consult the Kernel Git Commit 77ea917 and Kernel Git Commit c0410ad for the authoritative patch content.
Workarounds
- Unmount AFS volumes on systems that do not require them and unload the kafs module with modprobe -r kafs
- Blacklist the kafs module on hosts where AFS is not needed to prevent accidental loading
- Limit unprivileged local access on AFS-enabled hosts to reduce the population able to trigger the race
# Prevent the vulnerable AFS module from loading until patched
echo "blacklist kafs" | sudo tee /etc/modprobe.d/blacklist-kafs.conf
sudo modprobe -r kafs
# Verify kernel version after patching
uname -r
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
