External risk intelligence

SonicWall SonicOS SSL VPN Format String Vulnerability Causes Service Disruption

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2025-40600

The vulnerability affects the SSL VPN interface of SonicOS. SSL VPNs are designed to be internet-facing gateways that provide remote access to internal networks, making them inherently public-facing services by design.

Sonicwall Sonicos

7.1.1-7040 to before 7.3.0-7012

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in SonicOS, affecting its SSL VPN interface. This issue could allow an unauthenticated remote attacker to disrupt services. The primary concern is to confirm if our organization utilizes the affected technology and assess potential exposure.

Attackers can disrupt services remotely.
Critical SSL VPN flaw requires awareness.
Confirm relevance and assess potential exposure.

Attack Path

How an attacker could exploit the issue

An unauthenticated attacker on the network could exploit this vulnerability by sending specially crafted data to the SonicOS SSL VPN interface. This could allow them to disrupt services, potentially leading to unauthorized access or modification of sensitive information.

No authentication required.
Triggered via SSL VPN interface.
Leads to service disruption.

Live Threat

Current exploitation, exposure, and threat context

A remote, unauthenticated attacker could exploit a format string vulnerability within the SonicOS SSL VPN interface, potentially leading to a disruption of services. This could impact users' ability to access resources through the VPN when supported by the advisory.

VPN service disruption possible.
Unauthenticated network access.
Unavailability of remote access.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability impacts the SonicOS SSL VPN interface, a common internet-facing service for remote access. Responsibility likely falls to the platform or network security teams managing the SonicWall appliances, with potential involvement from vendor management if support contracts are impacted. The immediate first step should be to identify all instances of affected SonicWall SSL VPN interfaces, determine their exposure and criticality, and then confirm the accountable owner to plan a coordinated remediation effort.

Platform/Network teams own this vulnerability.
Verify external SSL VPN interface exposure.
Plan remediation based on identified risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

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Frequently asked questions

What is SonicOS and what role does it play?

SonicOS is the core operating system powering SonicWall firewalls and network security appliances. It manages traffic, enforces security policies, and provides critical features like the SSL VPN, which allows remote users to securely connect to private network resources. The vulnerability specifically impacts this VPN interface, which acts as a gateway between external users and internal systems across various TZ, NSa, and NSsp hardware models.

What is the format string vulnerability in CVE-2025-40600?

This vulnerability is classified as a 'Use of Externally-Controlled Format String' (CWE-134). It occurs when the software takes input from a user and processes it as part of a formatting command without proper validation. In this context, an attacker can manipulate these commands to confuse the software, which can lead to service instability or a complete crash of the SSL VPN interface.

How does an attacker trigger this vulnerability?

An attacker triggers this flaw by sending specially crafted data packets directly to the SSL VPN interface. Because the vulnerability exists in the interface itself, the attacker does not need to provide valid login credentials to initiate the attack. However, simply accessing the network is not enough; the crafted data must specifically target the way the interface handles string formatting to cause the disruption.

Is my organization at risk from this vulnerability?

If you use the affected versions of SonicOS, you should evaluate your risk. Halo Surface Signal notes that SSL VPNs are designed as internet-facing gateways to facilitate remote work, which inherently places this interface on the public internet. If your VPN portal is reachable from the outside, it is exposed to this vulnerability, making it a priority to verify your configuration and current version.

What steps should I take to address CVE-2025-40600?

Your first step is to inventory your infrastructure to identify every SonicWall appliance running the affected firmware. Consult your internal network or platform security team to verify the specific versions currently in use. Once identified, focus on confirming whether the SSL VPN interface is enabled and accessible. Use this data to coordinate with your security team to ensure the software is updated according to the vendor's guidance.

References

psirt.global.sonicwall.com/vuln-detail/SNWLID-2025-0013

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.