CVE-2026-0930: wolfSSHd Information Disclosure Vulnerability

CVE-2026-0930 Overview

CVE-2026-0930 is an out-of-bounds read vulnerability in wolfSSHd on Windows systems that occurs during terminal resize request handling. An authenticated user can trigger this vulnerability after establishing an SSH connection, causing adjacent stack memory to leak to the pseudo-console output. This represents a memory information disclosure issue that could potentially expose sensitive data stored in adjacent memory regions.

Critical Impact

Authenticated attackers can leak adjacent stack memory contents through crafted terminal resize requests, potentially exposing sensitive information from the wolfSSHd process memory.

Affected Products

• wolfSSHd on Windows (versions prior to the fix in PR #846)
• wolfSSH library implementations utilizing terminal resize functionality on Windows platforms

Discovery Timeline

• 2026-04-20 - CVE CVE-2026-0930 published to NVD
• 2026-04-21 - Last updated in NVD database

Technical Details for CVE-2026-0930

Vulnerability Analysis

This vulnerability is classified as CWE-126 (Buffer Over-read), a memory safety issue where the application reads data beyond the intended boundaries of a buffer. In the context of wolfSSHd on Windows, the flaw manifests when handling terminal resize requests from authenticated SSH clients.

When a connected user issues a terminal resize request, the wolfSSHd daemon processes the incoming window dimensions without properly validating the boundaries of the read operation. This allows the server to read beyond the allocated buffer, accessing adjacent stack memory. The leaked memory contents are then inadvertently transmitted to the pseudo-console output, making them visible to the attacker.

The requirement for prior authentication reduces the overall exposure, as an attacker must first establish a valid SSH session before attempting exploitation. However, any authenticated user—including those with limited privileges—could potentially extract sensitive information from the server's memory space.

Root Cause

The root cause of this vulnerability is improper boundary checking when processing terminal resize requests in the wolfSSHd Windows implementation. The code responsible for handling WINCH (window change) signals fails to validate that read operations stay within the bounds of the allocated buffer, resulting in an over-read condition.

This type of vulnerability commonly occurs when:

• Array indices or pointer arithmetic are not properly constrained
• Length parameters from external input are used without validation
• Platform-specific behavior differences (Windows vs. Unix) are not accounted for in boundary checks

Attack Vector

The attack requires network access and valid authentication credentials to the target wolfSSHd server. Once authenticated, an attacker can craft a malicious terminal resize request designed to trigger the out-of-bounds read condition.

The exploitation flow involves:

1. Establishing a legitimate SSH connection to the wolfSSHd server on Windows
2. Authenticating with valid credentials (low privilege is sufficient)
3. Sending a specially crafted terminal resize request that triggers the boundary violation
4. Receiving leaked stack memory contents in the pseudo-console output
5. Analyzing the leaked data for sensitive information such as memory addresses, credentials, or cryptographic material

The vulnerability requires network access and authentication but does not require user interaction, making it exploitable by any authenticated user with SSH access to the target system.

Detection Methods for CVE-2026-0930

Indicators of Compromise

• Unusual or excessive terminal resize requests from authenticated SSH sessions
• Anomalous pseudo-console output containing unexpected binary data or memory artifacts
• SSH session logs showing repeated resize operations from a single connection
• Memory access patterns indicating reads beyond expected buffer boundaries

Detection Strategies

• Monitor wolfSSHd logs for abnormal terminal resize request patterns from authenticated users
• Implement network-level inspection for SSH sessions with unusual window change signal frequency
• Deploy endpoint detection rules to identify memory read anomalies in wolfSSHd processes
• Use behavioral analysis to detect authenticated sessions performing suspicious resize operations

Monitoring Recommendations

• Enable verbose logging for wolfSSHd to capture terminal handling events
• Configure SIEM rules to alert on repetitive terminal resize requests within short timeframes
• Monitor pseudo-console output streams for unexpected data patterns indicating memory leakage
• Implement host-based intrusion detection for wolfSSHd process memory access anomalies

How to Mitigate CVE-2026-0930

Immediate Actions Required

• Review the GitHub Pull Request #846 for the official fix and apply the patch to affected wolfSSHd deployments
• Audit authenticated user accounts and limit SSH access to only necessary personnel
• Consider temporarily restricting terminal resize functionality if patch application is delayed
• Monitor existing SSH sessions for signs of exploitation attempts

Patch Information

The vulnerability has been addressed in GitHub Pull Request #846 for wolfssh. Organizations running wolfSSHd on Windows should review this pull request and update to a version that includes the fix. The patch corrects the boundary checking logic in the terminal resize request handler to prevent out-of-bounds read operations.

Workarounds

• Restrict SSH access to trusted users only until the patch can be applied
• Implement network segmentation to limit exposure of wolfSSHd servers to untrusted networks
• Monitor and audit all SSH connections for suspicious activity patterns
• Consider using alternative SSH implementations on Windows until the vulnerability is patched in your deployment

# Configuration example
# Restrict SSH access to specific trusted IP addresses (firewall example)
# Windows Firewall PowerShell command to limit wolfSSHd access
New-NetFirewallRule -DisplayName "Restrict wolfSSHd Access" -Direction Inbound -LocalPort 22 -Protocol TCP -RemoteAddress 192.168.1.0/24 -Action Allow
# Block all other SSH traffic
New-NetFirewallRule -DisplayName "Block External wolfSSHd" -Direction Inbound -LocalPort 22 -Protocol TCP -Action Block