Linux Kernel up to 7.2.6/7.3-rc1 smb/client improper synchronization

Summaryinfo

A vulnerability was found in Linux Kernel up to 7.2.6/7.3-rc1 and classified as critical. This issue affects the function smb3_zero_range/smb3_punch_hole/smb3_insert_range/smb3_collapse_range of the component smb/client. Such manipulation leads to improper synchronization. This vulnerability is uniquely identified as CVE-2026-98124. The attack can be launched remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 7.2.6/7.3-rc1. Affected by this issue is the function smb3_zero_range/smb3_punch_hole/smb3_insert_range/smb3_collapse_range of the component smb/client. The manipulation with an unknown input leads to a improper synchronization vulnerability. Using CWE to declare the problem leads to CWE-662. The product utilizes multiple threads or processes to allow temporary access to a shared resource that can only be exclusive to one process at a time, but it does not properly synchronize these actions, which might cause simultaneous accesses of this resource by multiple threads or processes. Impacted is confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: smb/client: invalidate fscache for fallocate range operations smb3_zero_range(), smb3_punch_hole(), smb3_insert_range(), and smb3_collapse_range() modify file contents through server-side range operations. These operations discard the affected page cache, but leave the FS-Cache cookie valid, so a later read may return data cached before the range operation. Fix this by invalidating FS-Cache after outstanding I/O has completed and before modifying the file on the server. Run the following as root on a CIFS mount with fsc enabled and an active CacheFiles backend: bash -c ' MNT=/mnt/cifs FILE="$MNT/repro" # Generate four 1 MiB random blocks: [A][B][C][D]. dd if=/dev/urandom of=/tmp/src bs=1M count=4 status=none # Expected contents after zeroing B: [A][zero][C][D]. cp /tmp/src /tmp/expected dd if=/dev/zero of=/tmp/expected bs=1M seek=1 count=1 \ conv=notrunc status=none cp /tmp/src "$FILE" # Populate FS-Cache, then discard the page cache. sync echo 1 > /proc/sys/vm/drop_caches cat "$FILE" > /dev/null sync echo 1 > /proc/sys/vm/drop_caches fallocate --zero-range -o 1M -l 1M "$FILE" if cmp -s /tmp/expected "$FILE"; then echo "readback: OK" else echo "readback: STALE DATA" fi ' Before this change, the readback differs from /tmp/expected: readback: STALE DATA After this change, it matches: readback: OK

The advisory is shared for download at git.kernel.org. This vulnerability is handled as CVE-2026-98124 since 09/25/2026. The exploitation is known to be easy. The attack may be launched remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/25/2026).

Upgrading to version 7.2.7 or 7.3-rc2 eliminates this vulnerability. Applying the patch 93c6e5a8d7c5071d586c1411596d5db5faad22b2/448ba0ae65ca61064183564d2983c9aa59bd6ba7 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.3-rc1

License

• open-source

Website

• Vendor: https://www.kernel.org/

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