CVE-2026-64380

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Linux Kernel POSIX SID Length Parsing Hardening

Publication date: 2026-07-25

Last updated on: 2026-09-08

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: harden POSIX SID length parsing posix_info_sid_size() reads sid[1] to obtain the subauthority count, but its existing boundary check still accepts buffers with only one remaining byte. Require two bytes before reading sid[1] so all client paths that reuse the helper reject truncated POSIX SIDs safely.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-07-25

Last Modified

2026-09-08

Generated

2026-09-24

AI Q&A

2026-07-25

EPSS Evaluated

2026-09-22

NVD

CVE-2026-64380

EUVD

EUVD-2026-48924

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	From 5.11 (inc) to 5.15.212 (exc)
linux	linux_kernel	From 5.16 (inc) to 6.1.178 (exc)
linux	linux_kernel	From 6.2 (inc) to 6.6.145 (exc)
linux	linux_kernel	From 6.7 (inc) to 6.12.96 (exc)
linux	linux_kernel	From 6.13 (inc) to 6.18.39 (exc)
linux	linux_kernel	From 6.19 (inc) to 7.1.4 (exc)
linux	linux_kernel	7.2
linux	linux_kernel	From 5.7 (inc) to 5.10.261 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel involves improper handling of POSIX SID (Security Identifier) length parsing in the SMB client. The function posix_info_sid_size() reads the subauthority count from sid[1] but lacks a proper boundary check, allowing buffers with only one byte to pass. This could lead to reading out-of-bounds data when truncated POSIX SIDs are processed.

Detection Guidance

This vulnerability is specific to the Linux kernel's SMB client implementation. Detection requires checking if your system is running a vulnerable kernel version. Use uname -a to check the kernel version and compare it against patched versions. If your kernel is older than the patched version, the system is likely vulnerable.

Impact Analysis

If exploited, this flaw could allow an attacker to cause a denial-of-service (DoS) condition or potentially execute arbitrary code on systems running vulnerable Linux kernel versions. Systems using SMB client functionality with untrusted network inputs are at higher risk.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards. It is a low-level kernel issue related to SMB client security in the Linux kernel, specifically involving improper boundary checks for POSIX SIDs. Compliance impacts would only occur if this flaw were exploited to compromise system integrity or data confidentiality, which is not indicated in the provided context.

Mitigation Strategies

Update the Linux kernel to the latest stable version that includes the fix for this vulnerability. This can typically be done through your distribution's package manager (e.g., apt upgrade, yum update). After updating, reboot the system to ensure the new kernel is loaded.

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