CVE-2025-9817: Wireshark SSH Dissector DOS Vulnerability

CVE-2025-9817 Overview

CVE-2025-9817 is a Null Pointer Dereference vulnerability affecting the SSH dissector in Wireshark versions 4.4.0 through 4.4.8. This vulnerability allows remote attackers to cause a denial of service condition by sending specially crafted SSH traffic that triggers a crash in the dissector component. The attack can be executed remotely without requiring any authentication or user interaction, making it a significant concern for organizations using Wireshark for network traffic analysis in production environments.

Critical Impact

Successful exploitation causes Wireshark to crash, disrupting network analysis operations and potentially allowing attackers to evade detection during active network monitoring sessions.

Affected Products

• Wireshark 4.4.0 through 4.4.8
• Wireshark 4.4.9-rc0 (release candidate)

Discovery Timeline

• 2025-09-03 - CVE-2025-9817 published to NVD
• 2025-12-05 - Last updated in NVD database

Technical Details for CVE-2025-9817

Vulnerability Analysis

This vulnerability is classified as CWE-476 (NULL Pointer Dereference), a memory corruption issue that occurs when the SSH dissector attempts to dereference a null pointer during packet processing. The SSH protocol dissector in Wireshark is responsible for parsing and displaying SSH traffic for network analysis purposes. When the dissector encounters malformed or specially crafted SSH packets, it fails to properly validate pointer references before use, resulting in an application crash.

The network-based attack vector with low complexity means that an attacker can trigger this vulnerability by simply transmitting malicious SSH packets to a network segment being monitored by a vulnerable Wireshark instance. No special privileges or user interaction are required to exploit this flaw. While the vulnerability does not result in confidentiality or integrity impacts, the availability impact is significant as it causes complete disruption of the Wireshark application.

Root Cause

The root cause of CVE-2025-9817 lies in insufficient null pointer validation within the SSH dissector code path. When parsing certain SSH protocol elements, the dissector fails to check whether a pointer is null before attempting to access the memory location it references. This programming error allows attackers to craft SSH packets that cause the vulnerable code path to be executed with a null pointer, resulting in a crash when the dereference operation is attempted.

Attack Vector

The attack exploits Wireshark's network packet capture and analysis functionality. An attacker can trigger the vulnerability through the following methods:

1. Live Capture Attack: Transmitting malicious SSH packets across a network segment where a vulnerable Wireshark instance is performing live packet capture
2. PCAP File Attack: Providing a maliciously crafted PCAP file containing SSH packets designed to trigger the null pointer dereference when opened for analysis
3. Remote Stream Analysis: If Wireshark is configured to analyze remote packet streams, attackers can inject malicious SSH traffic into the analyzed stream

The attack requires no authentication and can be executed by any network entity capable of sending packets to the monitored network segment. For detailed technical information, refer to the GitLab Wireshark Issue #20642 and the Wireshark Security Advisory 2025-03.

Detection Methods for CVE-2025-9817

Indicators of Compromise

• Unexpected Wireshark application crashes during network capture sessions, particularly when SSH traffic is present
• Core dump files or crash reports indicating null pointer dereference in SSH dissector functions
• Repeated Wireshark process terminations correlating with specific SSH traffic patterns on the network
• Log entries indicating abnormal termination of wireshark or tshark processes

Detection Strategies

• Monitor system logs and application crash reports for Wireshark null pointer dereference exceptions
• Implement automated restart monitoring for Wireshark processes to detect repeated crashes
• Use process monitoring tools to track Wireshark stability during active capture sessions
• Correlate Wireshark crashes with presence of unusual or malformed SSH packets in network traffic

Monitoring Recommendations

• Enable crash reporting and core dump generation for Wireshark installations to facilitate forensic analysis
• Implement application performance monitoring to detect sudden Wireshark process terminations
• Set up alerting for repeated Wireshark restarts within short time intervals
• Monitor network traffic for anomalous SSH packets that may indicate exploitation attempts

How to Mitigate CVE-2025-9817

Immediate Actions Required

• Upgrade all Wireshark installations to version 4.4.9 or later immediately
• If immediate patching is not possible, consider temporarily disabling the SSH dissector using Wireshark preferences
• Review network capture configurations and limit exposure to untrusted network segments
• Implement process monitoring to quickly detect and respond to Wireshark crashes

Patch Information

Wireshark has addressed this vulnerability in version 4.4.9. Organizations should upgrade to this version or later to remediate CVE-2025-9817. The security fix ensures proper null pointer validation in the SSH dissector code path before memory dereference operations.

For official patch details and download links, refer to the Wireshark Security Advisory 2025-03.

Workarounds

• Disable the SSH protocol dissector in Wireshark preferences if SSH analysis is not required
• Use alternative network analysis tools for environments with high SSH traffic until patching is complete
• Avoid opening untrusted PCAP files that may contain malicious SSH packets
• Limit network capture to trusted network segments where attacker-controlled traffic is unlikely

# Disable SSH dissector via Wireshark preferences
# Edit preferences file or use command line
wireshark -o "ssh.enable_dissector:FALSE"

# Or for tshark command-line captures
tshark --disable-protocol ssh -i eth0