CVE-2026-41476: Deskflow Use-After-Free Vulnerability

CVE-2026-41476 Overview

CVE-2026-41476 is a remote memory-safety vulnerability affecting Deskflow, a popular keyboard and mouse sharing application. The vulnerability exists in Deskflow's clipboard deserialization functionality, where a connected peer can trigger an out-of-bounds read by sending a malformed clipboard update. This memory corruption issue stems from insufficient validation of serialized clipboard data internal structure, allowing attackers to potentially access sensitive memory contents or crash the application.

Critical Impact

A remote attacker with low-privilege access to a connected Deskflow peer can exploit this vulnerability to read beyond allocated memory bounds, potentially exposing sensitive information or causing denial of service conditions.

Affected Products

• Deskflow versions prior to 1.26.0.138
• All platforms running vulnerable Deskflow clipboard sharing functionality
• Systems using Deskflow for cross-device keyboard and mouse sharing

Discovery Timeline

• April 24, 2026 - CVE-2026-41476 published to NVD
• April 28, 2026 - Last updated in NVD database

Technical Details for CVE-2026-41476

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), manifesting as an out-of-bounds read condition in Deskflow's clipboard handling code. The root issue lies in the clipboard deserialization process where malformed clipboard updates from connected peers are not properly validated before memory access operations occur.

The vulnerability is network-accessible, requiring only low-privilege authentication to a connected Deskflow peer. No user interaction is required for exploitation, and the attack complexity is low. An attacker successfully exploiting this vulnerability could achieve high impact on confidentiality, integrity, and availability of the affected system.

Root Cause

The vulnerability originates in the implementation of src/lib/deskflow/IClipboard.cpp. The ClipboardChunk::assemble() function in src/lib/deskflow/ClipboardChunk.cpp validates only the outer clipboard transfer size but fails to validate the internal structure of the serialized clipboard blob. As a result, malformed inner lengths pass validation and reach IClipboard::unmarshall() unchanged, where they can trigger out-of-bounds memory reads.

Attack Vector

The attack vector is network-based, exploiting the peer-to-peer communication channel between Deskflow instances. An attacker who has established a connection as a Deskflow peer can craft a malicious clipboard update containing manipulated internal length fields. When the victim's Deskflow instance processes this update, the unmarshall() function attempts to read memory based on the attacker-controlled length values, resulting in out-of-bounds memory access.

The attack sequence involves:

1. Establishing a connection as a Deskflow peer
2. Crafting a clipboard update with valid outer size but malformed inner structure
3. Sending the malicious clipboard data to the target peer
4. The target's IClipboard::unmarshall() processes the data without proper bounds checking
5. Out-of-bounds read occurs, potentially leaking memory contents or causing a crash

Detection Methods for CVE-2026-41476

Indicators of Compromise

• Unexpected crashes or segmentation faults in Deskflow processes during clipboard operations
• Abnormal network traffic patterns between Deskflow peers containing malformed clipboard data
• Memory access violations logged in system crash reports related to Deskflow
• Unusual clipboard synchronization failures between connected devices

Detection Strategies

• Monitor Deskflow process memory for anomalous access patterns or segmentation faults
• Implement network intrusion detection rules to identify malformed clipboard update packets
• Deploy endpoint detection solutions to monitor for exploitation attempts targeting clipboard handling
• Review system logs for repeated Deskflow crashes or unexpected terminations

Monitoring Recommendations

• Enable verbose logging in Deskflow to capture clipboard synchronization events
• Configure crash monitoring for Deskflow processes across all connected endpoints
• Implement network traffic analysis for Deskflow communication channels
• Set up alerting for abnormal memory consumption or access violation events in Deskflow

How to Mitigate CVE-2026-41476

Immediate Actions Required

• Upgrade all Deskflow installations to version 1.26.0.138 or later immediately
• Restrict network access to Deskflow services to trusted peers only
• Monitor connected Deskflow peers for suspicious activity
• Consider temporarily disabling clipboard sharing functionality until patches are applied

Patch Information

The vulnerability is fixed in Deskflow version 1.26.0.138. The patch addresses the insufficient validation in ClipboardChunk::assemble() by implementing proper bounds checking for internal clipboard data structures before they are processed by IClipboard::unmarshall(). For detailed patch information and the official security advisory, refer to the GitHub Security Advisory GHSA-3jp5-g964-cgmh.

Workarounds

• Disable clipboard sharing functionality in Deskflow configuration if immediate patching is not possible
• Implement network segmentation to isolate Deskflow traffic between trusted devices only
• Use firewall rules to restrict Deskflow connections to known and trusted IP addresses
• Monitor and audit all Deskflow peer connections for unauthorized access attempts

# Example: Restrict Deskflow traffic using firewall rules (Linux iptables)
# Allow Deskflow only from trusted peer IP
iptables -A INPUT -p tcp --dport 24800 -s TRUSTED_PEER_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 24800 -j DROP