ConnectWise ScreenConnect up to 25.2.3 ASP.NET Web Forms code injection

Summaryinfo

A vulnerability marked as critical has been reported in ConnectWise ScreenConnect up to 25.2.3. The impacted element is an unknown function of the component ASP.NET Web Forms. This manipulation causes code injection. This vulnerability is tracked as CVE-2025-3935. The attack is possible to be carried out remotely. Moreover, an exploit is present. It is recommended to apply a patch to fix this issue.

Detailsinfo

A vulnerability has been found in ConnectWise ScreenConnect up to 25.2.3 and classified as critical. Affected by this vulnerability is an unknown code of the component ASP.NET Web Forms. The manipulation with an unknown input leads to a code injection vulnerability. The CWE definition for the vulnerability is CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

ScreenConnect versions 25.2.3 and earlier versions may be susceptible to a ViewState code injection attack. ASP.NET Web Forms use ViewState to preserve page and control state, with data encoded using Base64 protected by machine keys.  It is important to note that to obtain these machine keys, privileged system level access must be obtained. If these machine keys are compromised, attackers could create and send a malicious ViewState to the website, potentially leading to remote code execution on the server.  The risk does not originate from a vulnerability introduced by ScreenConnect, but from platform level behavior.  This had no direct impact to ScreenConnect Client. ScreenConnect 2025.4 patch disables ViewState and removes any dependency on it.

It is possible to read the advisory at connectwise.com. This vulnerability is known as CVE-2025-3935 since 04/25/2025. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are unknown but an exploit is available. The attack technique deployed by this issue is T1059 according to MITRE ATT&CK.

It is declared as attacked. The CISA Known Exploited Vulnerabilities Catalog lists this issue since 06/02/2025 with a due date of 06/23/2025:

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Applying a patch is able to eliminate this problem.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2025-12502). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Type

• Network Management Software

Vendor

• ConnectWise

Name

• ScreenConnect

Version

• 25.2.0
• 25.2.1
• 25.2.2
• 25.2.3

CPE 2.3info

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CPE 2.2info

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Be aware that VulDB is the high quality source for vulnerability data.

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