# CVE-2026-99175: fsnotify: prevent mark additions during connector teardown

CVE-2026-99175 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99175, released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-99175
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0018
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 28, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99175

## Description

In the Linux kernel, the following vulnerability has been resolved:  fsnotify: prevent mark additions during connector teardown  fsnotify_destroy_marks() keeps a reference to its current mark while it drops conn->lock to destroy the mark. This stabilizes the forward-walk cursor, but does not prevent a new mark from being inserted before it. For example, an inotify watch re-added after IN_IGNORED sorts before the old, detached mark for the same group. The walk can miss the replacement and then detach the entire connector from the object.  The replacement is still on its group's marks_list and, for inotify, in the watch IDR. The group mutex no longer protects the connector's object from disappearing. An unprivileged fdinfo read racing the final detach can consequently call igrab(NULL):    BUG: KASAN: null-ptr-deref in igrab+0x24/0x100   Write of size 4 at addr 0000000000000148   Call Trace:    igrab+0x24/0x100    inotify_show_fdinfo+0x1dc/0x5e0    seq_show+0x397/0x690  Set a DESTROYING flag under conn->lock before starting the walk, and reject new marks on that connector with -ENOENT. The existing add-mark error paths undo the temporary group-list entry and the backend's watch allocation. Do not wait for teardown while holding the group mutex, which the destroyer needs. Once the old connector is detached, an add can install a fresh connector as before.  This closes the insertion race for all object types using the common connector teardown, without changing the mark reference or SRCU lifetime rules.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99175](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99175.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99175](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99175.md) | Nov 3, 2026 |

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Data as of 2026-11-08T06:59:42Z 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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