CVE-2026-0400: SonicWall SonicOS DOS Vulnerability

CVE-2026-0400 Overview

A post-authentication Format String vulnerability has been identified in SonicWall SonicOS that allows a remote attacker to crash affected firewall appliances. This vulnerability (CWE-134) occurs when user-controlled input is improperly processed as a format string argument, enabling an authenticated attacker to cause a denial of service condition on vulnerable SonicWall devices.

Critical Impact

Authenticated attackers can remotely crash SonicWall firewall appliances, disrupting network security infrastructure and potentially leaving networks unprotected during the outage period.

Affected Products

• SonicWall SonicOS (multiple versions)
• SonicWall NSA Series (NSA 2700, 2800, 3700, 3800, 4700, 4800, 5700, 5800, 6700)
• SonicWall NSSP Series (NSSP 10700, 11700, 13700, 15700)
• SonicWall NSv Series (NSv270, NSv470, NSv870)
• SonicWall TZ Series (TZ80, TZ270, TZ270W, TZ280, TZ370, TZ370W, TZ380, TZ470, TZ470W, TZ480, TZ570, TZ570P, TZ570W, TZ580, TZ670, TZ680)

Discovery Timeline

• February 24, 2026 - CVE-2026-0400 published to NVD
• February 26, 2026 - Last updated in NVD database

Technical Details for CVE-2026-0400

Vulnerability Analysis

This Format String vulnerability affects SonicOS, the operating system that powers SonicWall firewall appliances. The vulnerability requires authentication to exploit, meaning an attacker must first obtain valid credentials to access the firewall's management interface. Once authenticated, the attacker can supply specially crafted input containing format string specifiers that are improperly processed by vulnerable functions in SonicOS.

Format string vulnerabilities occur when user-supplied data is passed directly to formatting functions (such as printf() family functions) without proper sanitization. In this case, the vulnerability impacts availability rather than confidentiality or integrity, as successful exploitation results in a firewall crash rather than code execution or data disclosure.

Root Cause

The root cause of CVE-2026-0400 is improper handling of format string specifiers in user-controlled input within SonicOS (CWE-134: Use of Externally-Controlled Format String). When format specifiers such as %s, %n, or %x are embedded in user input and passed to a formatting function, the application interprets them as instructions rather than literal data, leading to unintended behavior including memory corruption and application crashes.

Attack Vector

The attack vector for this vulnerability is network-based, requiring the attacker to have authenticated access to the SonicWall management interface. The exploitation flow involves:

1. The attacker authenticates to the SonicWall firewall management interface using valid credentials
2. The attacker submits a request containing malicious format string specifiers to a vulnerable endpoint
3. The SonicOS firmware processes the input without proper sanitization
4. The format string specifiers cause memory access violations or corruption
5. The firewall service crashes, resulting in a denial of service condition

The attack requires high privileges (administrative access) but no user interaction, and can be executed remotely over the network. The impact is limited to availability, causing a complete crash of the firewall service.

Detection Methods for CVE-2026-0400

Indicators of Compromise

• Unexpected firewall reboots or service interruptions without scheduled maintenance
• Authentication logs showing repeated access attempts followed by system instability
• Crash dumps or core files containing format string-related memory violations
• Unusual HTTP/HTTPS requests to the management interface containing format specifiers (%s, %n, %x, %p)

Detection Strategies

• Monitor SonicWall management interface logs for requests containing format string patterns in input fields
• Implement network traffic analysis to detect anomalous requests to firewall management ports (typically 443 or 8443)
• Configure SIEM rules to correlate administrative authentication events with subsequent firewall crashes
• Review authentication logs for suspicious or unauthorized access to administrative accounts

Monitoring Recommendations

• Enable detailed logging on SonicWall management interface access and authentication events
• Set up alerts for unexpected firewall restarts or high-availability failover events
• Monitor administrative user activity for unusual patterns or access from unexpected source IPs
• Implement continuous availability monitoring for critical firewall appliances

How to Mitigate CVE-2026-0400

Immediate Actions Required

• Review the SonicWall Vulnerability Disclosure SNWLID-2026-0001 for the latest patch information
• Audit all administrative accounts and remove unnecessary privileged access
• Restrict management interface access to trusted IP addresses only
• Enable multi-factor authentication for administrative access where supported
• Monitor firewall stability closely for signs of exploitation attempts

Patch Information

SonicWall has released a security advisory addressing this vulnerability. Organizations should consult the official SonicWall PSIRT advisory for specific firmware versions containing the fix. Apply the recommended SonicOS firmware update to all affected appliances following your organization's change management procedures.

Workarounds

• Restrict administrative interface access to a dedicated management VLAN or specific trusted IP addresses
• Implement network segmentation to limit exposure of firewall management interfaces
• Use a VPN or jump host for remote administrative access rather than exposing management ports directly
• Enforce strong password policies and regular credential rotation for all administrative accounts
• Consider temporarily disabling remote management access if not operationally required

# Example: Restrict management interface access (SonicOS CLI)
# Consult SonicWall documentation for your specific firmware version
configure terminal
management http ip-range start 192.168.1.100 end 192.168.1.110
management https ip-range start 192.168.1.100 end 192.168.1.110
commit