Linux Kernel up to 6.16.3/6.17-rc2 can_idmap_mount missing initialization

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.16.3/6.17-rc2. It has been classified as critical. Affected is the function can_idmap_mount. This manipulation causes missing initialization. This vulnerability is registered as CVE-2025-39717. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.16.3/6.17-rc2 and classified as critical. Affected by this vulnerability is the function can_idmap_mount. The manipulation with an unknown input leads to a missing initialization vulnerability. The CWE definition for the vulnerability is CWE-456. The product does not initialize critical variables, which causes the execution environment to use unexpected values. The impact remains unknown. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: open_tree_attr: do not allow id-mapping changes without OPEN_TREE_CLONE As described in commit 7a54947e727b ('Merge patch series "fs: allow changing idmappings"'), open_tree_attr(2) was necessary in order to allow for a detached mount to be created and have its idmappings changed without the risk of any racing threads operating on it. For this reason, mount_setattr(2) still does not allow for id-mappings to be changed. However, there was a bug in commit 2462651ffa76 ("fs: allow changing idmappings") which allowed users to bypass this restriction by calling open_tree_attr(2) *without* OPEN_TREE_CLONE. can_idmap_mount() prevented this bug from allowing an attached mountpoint's id-mapping from being modified (thanks to an is_anon_ns() check), but this still allows for detached (but visible) mounts to have their be id-mapping changed. This risks the same UAF and locking issues as described in the merge commit, and was likely unintentional.

It is possible to read the advisory at git.kernel.org. This vulnerability is known as CVE-2025-39717 since 04/16/2025. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/09/2026).

The vulnerability scanner Nessus provides a plugin with the ID 261616 (Linux Distros Unpatched Vulnerability : CVE-2025-39717), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.16.4 or 6.17-rc3 eliminates this vulnerability. Applying the patch 69dbdc711d9130136824e3830191a6afffa0a1f0/9308366f062129d52e0ee3f7a019f7dd41db33df is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (261616) and CERT Bund (WID-SEC-2025-1988). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• Debian Linux
• Google Cloud Platform
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• NetApp FAS
• NetApp AFF
• NetApp ActiveIQ Unified Manager
• SUSE openSUSE
• RESF Rocky Linux
• Open Source Linux Kernel
• Microsoft Azure
• Dell Secure Connect Gateway
• IBM QRadar SIEM
• IBM Security Verify Access
• Dell NetWorker

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.16.0
• 6.16.1
• 6.16.2
• 6.16.3
• 6.17-rc1
• 6.17-rc2

License

• open-source

Website

• Vendor: https://www.kernel.org/

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