# CVE-2026-98124: smb/client: invalidate fscache for fallocate range operations

CVE-2026-98124 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-98124, released October 2, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98124
- Priority: Routine
- CVSS: 5.5 (Low)
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 25, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98124

## Description

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

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-98124](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98124.md) | Oct 2, 2026 |
| Linux | linux Debian 14 | 7.2.7-1 | [DEBIAN-CVE-2026-98124](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98124.md) | Oct 2, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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