CVE-2024-0565: Linux Kernel SMB Client DOS Vulnerability

CVE-2024-0565 Overview

An out-of-bounds memory read vulnerability has been identified in the Linux Kernel's SMB Client sub-component. The flaw exists in the receive_encrypted_standard function located in fs/smb/client/smb2ops.c. This vulnerability occurs due to an integer underflow condition affecting the memcpy length calculation, which can lead to out-of-bounds memory access and ultimately result in a denial of service condition.

Critical Impact

This integer underflow vulnerability in the Linux Kernel SMB Client can be exploited by an attacker on an adjacent network to cause out-of-bounds memory reads, leading to system crashes and denial of service. Systems using SMB encrypted connections are particularly at risk.

Affected Products

• Linux Kernel (versions prior to the fix, including 6.7 release candidates rc1-rc5)
• NetApp ONTAP Tools for VMware vSphere

Discovery Timeline

• January 15, 2024 - CVE-2024-0565 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-0565

Vulnerability Analysis

This vulnerability represents a classic integer underflow condition (CWE-191) in the Linux Kernel's SMB client implementation. The flaw manifests during the processing of encrypted SMB network traffic when the receive_encrypted_standard function calculates buffer lengths for memory copy operations.

When processing encrypted SMB responses, the function performs arithmetic operations on length values without adequate bounds checking. Under specific conditions, these calculations can result in an integer underflow, where a subtraction operation produces a negative value that wraps around to an unexpectedly large positive number when interpreted as an unsigned integer. This corrupted length value is then passed to memcpy, causing the function to read memory far beyond the intended buffer boundaries.

The attack requires the adversary to be positioned on an adjacent network and have low-level privileges, with some user interaction required for exploitation. When successfully triggered, the vulnerability can cause the kernel to access invalid memory regions, potentially exposing sensitive kernel memory contents or causing a kernel panic that crashes the entire system.

Root Cause

The root cause of this vulnerability lies in insufficient validation of arithmetic operations in the receive_encrypted_standard function within fs/smb/client/smb2ops.c. When processing encrypted SMB protocol data, the code performs subtraction operations on length values without verifying that the result remains within valid bounds. This allows specially crafted network packets to trigger an integer underflow condition, where the computed memcpy length becomes an extremely large value instead of the expected small positive integer.

Attack Vector

The vulnerability requires an attacker to be positioned on an adjacent network segment to the target system. The attack involves sending maliciously crafted encrypted SMB protocol messages that manipulate the length fields in a way that triggers the integer underflow condition. When the vulnerable kernel code processes these packets, the corrupted length value causes memcpy to read beyond the allocated buffer, potentially causing memory corruption or a kernel panic.

The attack scenario involves a system with an active SMB client connection using encryption. An attacker on the same network segment can inject or manipulate SMB encrypted responses to exploit the integer underflow in the length calculation, resulting in denial of service through kernel crash.

Detection Methods for CVE-2024-0565

Indicators of Compromise

• Unexpected kernel panics or system crashes on systems with active SMB connections
• Kernel log entries indicating memory access violations in the SMB client subsystem
• Crash dumps showing faults in receive_encrypted_standard or related SMB client functions
• Unusual network traffic patterns on SMB ports (445/TCP) from unexpected sources on the local network

Detection Strategies

• Monitor kernel logs for oops messages or panic traces involving fs/smb/client/smb2ops.c or receive_encrypted_standard
• Deploy network intrusion detection rules to identify anomalous SMB encrypted traffic patterns on local network segments
• Use kernel crash dump analysis tools to identify crashes related to SMB client memory operations
• Implement host-based monitoring to detect repeated SMB connection failures followed by system instability

Monitoring Recommendations

• Enable kernel crash dump collection (kdump) to capture detailed information about any kernel panics for forensic analysis
• Configure alerting on repeated SMB client errors or connection resets in system logs
• Monitor for unusual memory consumption or access patterns in kernel SMB client modules
• Implement network segmentation monitoring to detect unauthorized adjacent network access attempts

How to Mitigate CVE-2024-0565

Immediate Actions Required

• Update Linux Kernel to patched versions as provided by your distribution vendor
• Review and apply relevant security advisories from Red Hat, Debian, and NetApp
• Temporarily disable SMB encryption if not required and system cannot be immediately patched
• Implement network segmentation to limit adjacent network attack surface

Patch Information

Multiple Linux distribution vendors have released patches addressing this vulnerability. Administrators should consult the following security advisories for patch information specific to their environment:

• Red Hat Security Advisory RHSA-2024:1188
• Red Hat Security Advisory RHSA-2024:1404
• Red Hat Security Advisory RHSA-2024:1532
• Red Hat Security Advisory RHSA-2024:2394
• Debian LTS Announcement June 2024
• NetApp Security Advisory NTAP-20240223-0002

For additional technical details, refer to Red Hat Bugzilla Report #2258518 and the Stable Commits Message #328851.

Workarounds

• Restrict SMB client usage to trusted network segments with strict access controls
• Disable SMB encryption temporarily if the business impact is acceptable and patching is not immediately possible
• Implement network-level filtering to limit which systems can communicate via SMB protocols
• Consider using alternative file sharing protocols where SMB encryption is not critical

# Check current kernel version for patch status
uname -r

# Verify SMB client module status
lsmod | grep cifs

# Review active SMB mounts that may use encryption
mount | grep cifs

# Check for available kernel updates (RHEL/CentOS)
yum check-update kernel

# Check for available kernel updates (Debian/Ubuntu)
apt list --upgradable | grep linux-image