CVE-2026-4113 Overview
An observable response discrepancy vulnerability has been identified in SonicWall SMA1000 series appliances that enables remote attackers to enumerate SSL VPN user credentials. This information disclosure flaw (CWE-204) allows unauthenticated attackers to distinguish between valid and invalid usernames based on differences in application responses, potentially facilitating targeted brute-force attacks against confirmed user accounts.
Critical Impact
Remote attackers can enumerate valid SSL VPN user accounts on SonicWall SMA1000 appliances without authentication, enabling targeted credential attacks.
Affected Products
- SonicWall SMA1000 Series Appliances
- SSL VPN Components on SMA1000 Devices
Discovery Timeline
- April 9, 2026 - CVE-2026-4113 published to NVD
- April 9, 2026 - Last updated in NVD database
Technical Details for CVE-2026-4113
Vulnerability Analysis
This vulnerability falls under CWE-204: Observable Response Discrepancy, a class of information disclosure weaknesses where an application behaves differently based on the validity of input data. In the context of the SonicWall SMA1000 series, the SSL VPN authentication mechanism exhibits distinguishable responses when processing authentication requests with valid versus invalid usernames.
Observable response discrepancies commonly manifest through timing differences, distinct error messages, or varying HTTP response codes. Attackers can systematically submit authentication requests with candidate usernames and analyze the responses to build a list of valid user accounts. Once valid usernames are identified, attackers can focus password guessing or credential stuffing attacks specifically on confirmed accounts, significantly improving attack efficiency.
Root Cause
The root cause of this vulnerability lies in the SSL VPN authentication handler's failure to provide uniform responses regardless of username validity. The application likely performs different processing paths or returns distinguishable feedback when a submitted username exists in the system versus when it does not. Proper implementation should ensure that authentication failures produce identical responses in timing, content, and structure whether the username or password is incorrect.
Attack Vector
An attacker can exploit this vulnerability remotely without authentication by sending crafted authentication requests to the SSL VPN login endpoint. The attack methodology involves submitting a list of potential usernames while carefully analyzing server responses for discrepancies. These differences could include variations in response time, error message text, HTTP status codes, or page content length.
Once the attacker compiles a list of valid usernames, they can execute targeted attacks such as password spraying (attempting common passwords against all valid accounts), credential stuffing (using leaked credentials from other breaches), or spear-phishing campaigns targeting specific users.
For detailed technical information, refer to the SonicWall Vulnerability Advisory SNWLID-2026-0003.
Detection Methods for CVE-2026-4113
Indicators of Compromise
- Unusual volume of failed authentication attempts against the SSL VPN login endpoint with varying usernames but identical or empty passwords
- Sequential or rapid authentication requests originating from single IP addresses or address ranges
- Authentication logs showing systematic testing of common or dictionary-based usernames
Detection Strategies
- Monitor SSL VPN authentication logs for patterns indicative of username enumeration such as high failure rates with diverse usernames
- Implement rate limiting detection rules to identify brute-force enumeration attempts against the authentication endpoint
- Deploy network intrusion detection signatures to identify automated enumeration tools targeting SonicWall appliances
Monitoring Recommendations
- Enable verbose logging on SMA1000 appliances to capture all authentication attempts including source IP, timestamp, and username
- Configure SIEM alerts for threshold-based detection when authentication failures from a single source exceed normal baselines
- Regularly review authentication logs for anomalous patterns that may indicate reconnaissance activity
How to Mitigate CVE-2026-4113
Immediate Actions Required
- Consult the SonicWall Vulnerability Advisory SNWLID-2026-0003 for official patch availability and installation instructions
- Implement IP-based rate limiting on the SSL VPN login endpoint to slow enumeration attempts
- Enable multi-factor authentication (MFA) to mitigate the impact of credential compromise resulting from enumeration
- Review and strengthen password policies for all VPN user accounts
Patch Information
SonicWall has released a security advisory addressing this vulnerability. Organizations should apply the latest firmware updates to affected SMA1000 series appliances as directed in the SonicWall Vulnerability Advisory SNWLID-2026-0003. Contact SonicWall support for guidance on obtaining and deploying the appropriate security patches for your environment.
Workarounds
- Restrict SSL VPN login endpoint access to trusted IP ranges using firewall rules where operationally feasible
- Implement account lockout policies after a defined number of failed authentication attempts
- Deploy a Web Application Firewall (WAF) with rules to detect and block enumeration patterns
- Consider placing additional network security controls such as VPN concentrators or jump hosts in front of the SMA1000 appliance
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
