Linux Kernel Vulnerability: CVE-2026-64257 - Reject Overlapping Data Areas in SMB2 Responses

Executive Summary

A vulnerability in the Linux kernel, tracked as CVE-2026-64257, has been identified in the SMB2 response handling. This vulnerability can be exploited by an attacker to make an invalid response appear as if it has no data area, which could lead to security issues. The vulnerability affects multiple Linux kernel versions, and users are advised to update to the latest version to mitigate the risk. The severity of this vulnerability is not explicitly stated, but it is considered important to address.

Technical Analysis

The vulnerability is classified as an issue with the SMB2 response handling in the Linux kernel. Specifically, it involves the handling of overlapping data areas in SMB2 responses. The root cause of the vulnerability is that the overlap handling in `__smb2_calc_size()` clears `data_length`, which can make an invalid response appear to have no data area and thus qualify for an exception.

How It Gets Exploited

An attacker would need to send a crafted SMB2 response to the Linux kernel, specifically designed to trigger the overlap handling in `__smb2_calc_size()`. This would involve creating a response where the data areas overlap in such a way that `data_length` is cleared, making the response appear valid but actually bypassing security checks. The attacker would gain the ability to manipulate the SMB2 response handling, potentially leading to security issues such as denial of service or code execution.

Impact Assessment

The vulnerability affects various Linux kernel versions, including 5.10, 5.15, and 7.2-rc3. An attacker could exploit this vulnerability to cause a denial of service or potentially achieve code execution. The CVSS score for this vulnerability is not provided, but it is considered important to address.

Recommended Actions

To mitigate this vulnerability, users should update their Linux kernel to the latest version available. Specifically, for affected versions: - Update to a version beyond 445ece263131780dee273d727a4d6f11934feec7 for some branches. - Update to version 7.2-rc4 or later for 7.2-rc3 and earlier. - Apply patches or updates provided by your Linux distribution.

Sources

- National Vulnerability Database (NVD): https://nvd.nist.gov/vuln/detail/CVE-2026-64257