CVE-2026-74259 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
cifs: remove all cifs files before kill super
Cifs files may be put into fileinfo_put_wq during umounting cifs. After umount done, cifsFileInfo_put_final is called, which cause following BUG:
BUG: kernel NULL pointer dereference, address: 0000000000000000 ... [ 134.222152] list_lru_add+0x64/0x1a0
[ 134.222399] ? cifs_put_tcon+0x171/0x340 [cifs]
[ 134.222772] d_lru_add+0x44/0x60
[ 134.222997] dput+0x1fc/0x210
[ 134.223213] cifsFileInfo_put_final+0x11a/0x140 [cifs]
[ 134.223576] process_one_work+0x17c/0x320
[ 134.223843] worker_thread+0x188/0x280
[ 134.224084] ? __pfx_worker_thread+0x10/0x10
[ 134.224366] kthread+0xcc/0x100
[ 134.224576] ? __pfx_kthread+0x10/0x10
[ 134.224827] ret_from_fork+0x30/0x50
[ 134.225063] ? __pfx_kthread+0x10/0x10
[ 134.225328] ret_from_fork_asm+0x1b/0x30
This can be reproduce by following: unshare -n bash -c " mkdir -p ${CIFS_MNT}
ip netns attach root 1 ip link add eth0 type veth peer veth0 netns root ip link set eth0 up ip -n root link set veth0 up ip addr add 192.168.0.2/24 dev eth0 ip -n root addr add 192.168.0.1/24 dev veth0 ip route add default via 192.168.0.1 dev eth0 ip netns exec root sysctl net.ipv4.ip_forward=1 ip netns exec root iptables -t nat -A POSTROUTING -s 192.168.0.2 -o ${DEV} -j MASQUERADE
mount -t cifs ${CIFS_PATH} ${CIFS_MNT} -o
vers=3.0,sec=ntlmssp,credentials=${CIFS_CRED},rsize=65536,wsize=65536,cache=none,echo_interval=1
touch ${CIFS_MNT}/a.txt
ip netns exec root iptables -t nat -D POSTROUTING -s 192.168.0.2 -o ${DEV} -j MASQUERADE
" umount ${CIFS_MNT}
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the Linux kernel's cifs filesystem implementation where improper handling of file cleanup during unmount operations leads to a kernel NULL pointer dereference. The issue occurs when cifs files are processed through the fileinfo_put_wq workqueue during the unmount process, creating a race condition between file reference management and superblock destruction. When the umount operation completes, cifsFileInfo_put_final function is invoked which attempts to access a NULL pointer, resulting in kernel panic and system crash. The vulnerability stems from the improper ordering of cleanup operations where files that were queued for processing may still be referenced when the superblock is being destroyed, creating a scenario where kernel memory management structures become corrupted.
The technical flaw manifests as a direct violation of proper resource lifecycle management within the kernel's filesystem subsystem. During normal operation, cifs files are added to a workqueue (fileinfo_put_wq) for asynchronous cleanup processing while the filesystem is still operational. However, when umount completes, the superblock destruction process begins before all queued cleanup operations can complete properly. The cifsFileInfo_put_final function attempts to perform list_lru_add operations on what should be valid data structures but instead encounters NULL pointers, triggering the kernel's memory protection mechanisms and resulting in immediate system termination. This represents a classic case of improper synchronization between asynchronous work processing and resource destruction phases.
The operational impact of this vulnerability is severe as it can cause complete system crashes when attempting to unmount cifs filesystems under specific network conditions. Attackers could potentially exploit this by creating controlled network scenarios that trigger the race condition, leading to denial of service attacks against systems running cifs mounts. The vulnerability affects any Linux system using cifs filesystem with version 3.0 or higher and is particularly dangerous in server environments where cifs shares are frequently mounted and unmounted. The crash occurs at the kernel level, bypassing user-space protections and making it impossible to recover without system reboot.
The fix implemented addresses this by ensuring all cifs files are properly removed from the workqueue before the superblock destruction process begins. This involves modifying the umount sequence to flush all pending work items in fileinfo_put_wq before proceeding with final cleanup operations, preventing the race condition that leads to NULL pointer dereference. The solution aligns with security best practices for kernel resource management and follows established patterns for proper asynchronous workqueue handling. From an ATT&CK perspective, this vulnerability would be classified under privilege escalation or denial of service techniques where system stability is compromised through improper kernel memory management. The vulnerability maps to CWE-476 which describes NULL pointer dereference conditions in software, and demonstrates the importance of maintaining proper synchronization between resource allocation and deallocation processes in kernel space operations.