Bug 2507076 (CVE-2026-64391)

Summary: CVE-2026-64391 kernel: ksmbd: use opener credentials for ADS I/O
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: unspecified Docs Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in ksmbd, the in-kernel Server Message Block (SMB) daemon. This vulnerability allows a remote attacker to bypass security restrictions by incorrectly handling credentials for Alternate Data Streams (ADS) input/output (I/O) operations. Instead of using the credentials established when the SMB handle was opened, ksmbd uses the current task's credentials. This misconfiguration can lead to a bypass of inode permissions and Linux Security Module (LSM) policies, potentially resulting in privilege escalation and unauthorized access to system resources.
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Description OSIDB Bzimport 2026-07-25 10:03:43 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: use opener credentials for ADS I/O

Alternate data streams are stored as xattrs. Unlike regular file I/O,
their read and write paths therefore call VFS xattr helpers which recheck
inode permissions and LSM policy using the current task credentials.

Run ADS I/O with the credentials captured when the SMB handle was opened.
Comment 1 Mauro Matteo Cascella 2026-07-29 17:15:58 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072527-CVE-2026-64391-ae65@gregkh/T