CVE-2025-22869: Go SSH Denial of Service Vulnerability

CVE-2025-22869 Overview

SSH servers which implement file transfer protocols are vulnerable to a denial of service attack from clients which complete the key exchange slowly, or not at all, causing pending content to be read into memory, but never transmitted.

Critical Impact

This vulnerability can be exploited to cause service disruptions and resource exhaustion on affected servers.

Affected Products

• Go SSH

Discovery Timeline

• 2025-02-26T08:14:24.997 - CVE CVE-2025-22869 published to NVD
• 2025-05-01T19:28:20.740 - Last updated in NVD database

Technical Details for CVE-2025-22869

Vulnerability Analysis

The vulnerability exists in the handling of SSH connections when key exchanges are initiated by clients but completed very slowly or not completed at all. This behavior leads to the accumulation of pending data in memory, which is never transmitted, leading to potential denial of service.

Root Cause

The issue is caused by improper handling and validation of client-side initiation of key exchanges, allowing clients to control the server's memory utilization.

Attack Vector

Network-based exploitation from a remote, unauthenticated attacker.

# Example exploitation code (sanitized)
while true; do
  ssh -oKexAlgorithms=+slow-exchange target-ssh-server
done

Detection Methods for CVE-2025-22869

Indicators of Compromise

• Unexpected increase in memory usage
• High number of incomplete SSH sessions
• Log entries indicating aborted key exchanges

Detection Strategies

Utilize intrusion detection systems to monitor for incomplete key exchanges and abnormal memory utilization patterns in SSH server logs.

Monitoring Recommendations

Implement logging policies to capture and audit SSH connection attempts that do not complete the key exchange process.

How to Mitigate CVE-2025-22869

Immediate Actions Required

• Deploy rate limiting on SSH connection attempts.
• Implement stricter timeout settings for incomplete sessions.
• Enable memory and resource monitoring to detect early signs of exploitation.

Patch Information

Refer to the official Go advisory and patch details here.

Workarounds

Utilize configuration settings to manage and limit resource usage, ensuring consistent memory management.

# Configuration example
MaxStartups 10:30:60
LoginGraceTime 20s