CVE-2024-12086: Samba Rsync Information Disclosure Flaw

CVE-2024-12086 Overview

A significant information disclosure vulnerability has been identified in rsync, the widely-used file synchronization utility. This flaw allows a malicious rsync server to enumerate and reconstruct the contents of arbitrary files from a client's machine during file transfer operations. The vulnerability exploits the checksum comparison mechanism that rsync uses to optimize file transfers, enabling byte-by-byte data reconstruction through specially crafted checksum responses.

Critical Impact
A malicious rsync server can extract sensitive file contents from client machines, potentially exposing credentials, private keys, configuration files, and other confidential data without the user's knowledge.

Affected Products

Samba rsync (all vulnerable versions)
Red Hat OpenShift Container Platform 4.0
Red Hat Enterprise Linux 6.0, 7.0, 8.0, 9.0, 10.0
AlmaLinux 8.0, 9.0, 10.0
Arch Linux
Gentoo Linux
NixOS
SUSE Linux
Triton DataCenter SmartOS

Discovery Timeline

January 14, 2025 - CVE-2024-12086 published to NVD
November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2024-12086

Vulnerability Analysis

This vulnerability targets the fundamental mechanism rsync uses for efficient file synchronization. When files are being copied from a client to a server, the rsync server sends checksums of local data blocks to the client for comparison. The client then uses these checksums to determine which data blocks need to be transmitted to the server.

The flaw exists in how the client processes and responds to these checksum requests. A malicious server can send specially constructed checksum values for files that the client did not intend to synchronize. By analyzing the client's responses to these crafted checksums, an attacker can systematically reconstruct the contents of arbitrary files on the client machine, byte-by-byte. This is classified as CWE-390 (Detection of Error Condition Without Action), indicating that error conditions related to checksum mismatches are not properly handled.

Root Cause

The root cause lies in the insufficient validation of checksum requests from the server. The rsync client does not adequately verify that checksum requests correspond only to files explicitly intended for transfer. This allows a rogue server to request checksums for arbitrary files accessible to the rsync client process. The client's responses to these checksum queries inadvertently leak information about the file contents, enabling gradual data exfiltration through a side-channel attack.

Attack Vector

The attack is network-based and requires the victim to initiate an rsync operation to a malicious server. The attack scenario typically involves:

An attacker sets up a rogue rsync server or compromises an existing one
A victim connects to the malicious server to push files (client-to-server transfer)
The malicious server sends crafted checksum requests targeting sensitive files on the client
The client responds with checksum comparison results for files it can access
The attacker analyzes responses to reconstruct file contents byte-by-byte

The attack requires no user interaction beyond the initial rsync connection and works without requiring authentication or special privileges on the target system. However, the attack complexity is considered high due to the need for the attacker to control or compromise an rsync server that the victim connects to.

Detection Methods for CVE-2024-12086

Indicators of Compromise

Unusual rsync connections to unknown or untrusted servers
Rsync sessions with abnormally long duration or high volume of checksum exchanges
Network traffic analysis showing unexpected file path references in rsync protocol communications
Server-side logs indicating checksum requests for files outside the expected transfer scope

Detection Strategies

Monitor rsync client connections for connections to non-whitelisted servers
Implement network-level monitoring to detect anomalous rsync protocol behavior
Deploy endpoint detection rules to identify rsync processes accessing sensitive files unexpectedly
Use file integrity monitoring to detect if sensitive files are being read by rsync processes

Monitoring Recommendations

Enable verbose logging for rsync operations to track file access patterns
Configure network security monitoring to alert on rsync connections to external or unknown destinations
Implement application-level firewalls to restrict rsync server destinations
Review rsync configuration files and scripts for hardcoded server addresses that could be targets for compromise

How to Mitigate CVE-2024-12086

Immediate Actions Required

Update rsync to the latest patched version available for your distribution
Audit current rsync usage to identify client-to-server transfer operations
Restrict rsync operations to trusted, verified servers only
Consider using SSH tunneling with host key verification for all rsync transfers

Patch Information

Security patches have been released by multiple vendors. Refer to the following advisories for distribution-specific updates:

Workarounds

Avoid using rsync to push files to untrusted or unverified servers
Use --checksum with caution and prefer --whole-file mode when connecting to external servers to disable incremental checksum-based transfers
Implement network segmentation to restrict rsync traffic to known, trusted endpoints
Use alternative secure file transfer methods (such as scp or SFTP) when connecting to external systems until patches are applied

bash

# Restrict rsync to trusted servers only via SSH with host key verification
rsync -avz -e "ssh -o StrictHostKeyChecking=yes" /local/path/ user@trusted-server:/remote/path/

# Use --whole-file to disable checksum-based delta transfers (mitigates this vulnerability)
rsync -avz --whole-file /source/ rsync://server/destination/