Authentication weaknesses
The application does not reliably check that someone is who they claim to be.
CWE-287 · CISA KEV
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Exploited. On CISA's list since 2025-06-02.
ConnectWise ScreenConnect Improper Authentication Vulnerability
CVE-2025-3935 · ConnectWise ScreenConnect · Published 2025-04-25
How bad would it be?
7.2 out of 10
CVSS rates it high.
How likely is it to be used?
3.6%
Estimated chance of exploitation in the next 30 days, higher than 89% of all scored flaws (EPSS, 2026-10-29).
Is it already being used?
Yes
CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 494 days ago (2025-06-23).
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
ConnectWise ScreenConnect contains an improper authentication vulnerability. This vulnerability could allow a ViewState code injection attack, which could allow remote code execution if machine keys are compromised.
What the flaw 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.
From the NVD.
Fixes and advisories
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Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.
Insecure deserialization
Rebuilding objects from untrusted saved data can trigger unintended behaviour.
CWE-502 · NVD record: 7d616e1a-3288-43b1-a0dd-0a65d3e70a49
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CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.
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Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.