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Critical Linux Kernel KSMBD Vulnerability Detected by ZDI

Updated on 2022-12-31: Linux Kernel Vulnerability

Researchers from the ZDI (Zero Day Initiative) have detected a critical use-after-free remote code execution vulnerability in Linux kernel ksmbd. The issue lies in the way SMB2_TREE_DISCONNECT commands are processed.

Note

  • In a pre-holiday “Grinch move”, ZDI released limited details on this vulnerability and likely included a likely inflated CVSS of 10. Parties involved did not bother to assign a CVE number. ksmbd is a kernel-level implementation of the SMB protocol, in part replacing the existing user space implementation provided by SAMBA. It has only been included in quite recent versions of Linux, and needs to be enabled for your system to be vulnerable. Patches have been available for a few months now, and the chance of you running a vulnerable version are low, but better guidance is needed to identify affected kernels. As a rule of thumb: Linux-based network storage systems, which implement SMB file sharing, and were procured this year, are possibly affected.
  • The bug affects the in-kernel SMB server designed to augment Samba, on systems running the Linux 5.15 kernel, such as Ubuntu 22.04. Odds are your enterprise apps are running on older kernels such as RHEL 8, so getting ahead of this may not be too bad. Check the kernel versions you have deployed, then for those running the 5.15 kernel, target first those with the ksmb module loaded.

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Overview

Experts warned of a critical Linux kernel vulnerability that leads to remote code execution attacks on SMB servers. The flaw only affects SMB servers using the ‘ksmbd’ module.

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