# CVE-2026-99179: watch_queue: Fix note pool publication race in watch_queue_set_size()

CVE-2026-99179 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99179, released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-99179
- Priority: Routine
- CVSS: 5.5 (Moderate)
- 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-2026-99179

## Description

In the Linux kernel, the following vulnerability has been resolved:  watch_queue: Fix note pool publication race in watch_queue_set_size()  There is a race between watch_queue_set_size() and post_one_notification(). watch_queue_set_size() publishes wqueue->notes, notes_bitmap, nr_pages and nr_notes with plain stores, and post_one_notification() reads them with plain loads under a different lock, so nothing orders the four stores against the poster's loads: depending on the build, notes can be stored last (gcc 14 on x86-64 does this).  Since keyctl_watch_key() lets a watch attach to a queue before it is sized, post_one_notification() can already be running on another CPU at that moment: it reads nr_notes > 0, passes its bounds check, and then reads notes while it is still NULL, dereferencing notes[0].  An unprivileged user triggers this reliably by watching one of its own keys through a notification pipe and racing ioctl(IOC_WATCH_QUEUE_SET_SIZE) on that pipe against keyctl(KEYCTL_SETPERM) on the key from another CPU, triggering:    BUG: kernel NULL pointer dereference, address: 0000000000000000   RIP: 0010:post_one_notification.isra.0+0xa2/0x1e0   Call Trace:    __post_watch_notification+0x148/0x180    keyctl_setperm_key+0x119/0x130    do_syscall_64+0x108/0x4c0    entry_SYSCALL_64_after_hwframe+0x77/0x7f   Kernel panic - not syncing: Fatal exception in interrupt  Fix this by publishing nr_notes last with smp_store_release(), and by reading it once with smp_load_acquire() in post_one_notification() before the bitmap and the page array are touched.  A poster that observes a non-zero nr_notes then also observes the pool behind it; one that observes zero drops the notification as before.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99179](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99179.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99179](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99179.md) | Nov 3, 2026 |

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Data as of 2026-11-09T01:18:40Z 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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