CVE-2024-26952: Linux Kernel Buffer Overflow Vulnerability

CVE-2024-26952 Overview

CVE-2024-26952 is an out-of-bounds vulnerability in the Linux kernel's ksmbd in-kernel SMB3 server. The flaw resides in request handlers that fail to properly validate the buffer offset field of incoming SMB requests. When the buffer offset is invalid, the kernel can read or write memory outside the intended boundaries. The issue is tracked under [CWE-120] (Buffer Copy without Checking Size of Input) and [CWE-125] (Out-of-Bounds Read). The fix sets a minimum value for the buffer offset to ->Buffer offset before validating buffer length.

Critical Impact
A local authenticated attacker with access to an SMB share served by ksmbd can trigger out-of-bounds memory access, leading to kernel memory disclosure, corruption, or denial of service.

Affected Products

Linux kernel versions containing the ksmbd SMB3 server prior to the patched stable releases
Debian LTS distributions shipping vulnerable kernel builds
Server and workstation deployments exposing ksmbd shares to authenticated users

Discovery Timeline

2024-05-01 - CVE-2024-26952 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-26952

Vulnerability Analysis

The vulnerability affects ksmbd, the in-kernel SMB3 file server introduced in Linux 5.15. Multiple SMB2 request handlers parse client-supplied structures containing a buffer offset and buffer length. The handlers used these fields to locate variable-length data within the request payload.

Before the patch, the code did not enforce a minimum value for the buffer offset. An attacker could supply an offset value that pointed before the legitimate data region or beyond the request boundary. The subsequent length-based validation operated on attacker-controlled arithmetic, allowing out-of-bounds memory access during request processing.

Because ksmbd runs in kernel context, the resulting memory corruption or disclosure occurs at the highest privilege level on the host. The vulnerability impacts confidentiality, integrity, and availability of the kernel.

Root Cause

The root cause is missing input validation on the buffer offset field in several SMB2 request parsers. The handlers trusted the client-supplied offset without confirming it referenced a position within the expected payload area. The upstream fix establishes a minimum buffer offset equal to the start of the request's Buffer field, ensuring length calculations operate on a sane base before validation.

Attack Vector

Exploitation requires local access with valid SMB credentials on a host running ksmbd. An authenticated user sends a crafted SMB2 request containing a malformed buffer offset. The kernel then dereferences memory outside the intended request buffer during length validation or payload copying.

No public exploitation code or proof of concept is referenced in the advisory. The vulnerability mechanism is described in the upstream kernel commits and the Debian LTS Announcement.

Detection Methods for CVE-2024-26952

Indicators of Compromise

Unexpected ksmbd kernel oops or panic messages in dmesg referencing SMB2 request parsing functions
Unusual SMB session terminations originating from authenticated clients on hosts running ksmbd
Kernel memory access faults logged near ksmbd_smb2_* symbols in crash reports

Detection Strategies

Inventory kernel versions across Linux hosts and flag systems running unpatched builds with ksmbd loaded
Monitor for the ksmbd module being loaded on systems that do not require SMB serving
Correlate SMB authentication events with subsequent kernel-level faults to identify potential exploitation attempts

Monitoring Recommendations

Enable kernel audit logging for module load events covering ksmbd.ko
Forward dmesg and /var/log/kern.log to a centralized log platform for anomaly review
Alert on repeated SMB session failures from a single authenticated source against ksmbd shares

How to Mitigate CVE-2024-26952

Immediate Actions Required

Apply the upstream kernel patches referenced in the kernel.org commits and reboot affected systems
If patching is not immediately possible, unload the ksmbd module on hosts that do not require SMB server functionality
Restrict SMB share access to trusted authenticated users and segment SMB traffic on isolated network paths

Patch Information

The fix is committed across multiple stable branches. Reference commits include 0c5541b4c980, 2dcda336b6e8, 39bdc4197acf, 480469f145e5, ad6480c9a5d8, and c6cd2e8d2d9a. Debian users should consult the Debian LTS Announcement for distribution-specific package updates.

Workarounds

Disable ksmbd and use a userspace SMB server such as Samba on hosts where kernel updates cannot be applied promptly
Blacklist the ksmbd module via /etc/modprobe.d/ to prevent automatic loading
Limit SMB access at the network firewall to known administrative subnets until the kernel patch is deployed

bash

# Configuration example
# Prevent the vulnerable ksmbd module from loading
echo "blacklist ksmbd" | sudo tee /etc/modprobe.d/ksmbd-blacklist.conf
sudo modprobe -r ksmbd

# Verify the running kernel version after patching
uname -r