Security readout for executives and security teams
Plain-English summary
ScreenConnect servers at version 25.2.3 or earlier can be exposed to ASP.NET ViewState code injection if attackers obtain the server’s machine keys. That condition could allow remote code execution on the server. CISA lists this CVE in KEV, so treat affected servers as a time-sensitive risk.
Executive priority
High priority. Remote management software is sensitive infrastructure, and CISA KEV confirms known exploitation. Upgrade affected ScreenConnect servers promptly and verify no exposed legacy instances remain.
Technical view
The issue concerns ASP.NET Web Forms ViewState handling. If machine keys are compromised, an attacker can craft malicious ViewState data that the server may process, potentially causing code execution. ConnectWise says ScreenConnect 2025.4 disables ViewState and removes dependency on it. The source describes no direct impact to ScreenConnect Client.
Likely exposure
Exposure is most relevant to ScreenConnect server installations running 25.2.3 or earlier, especially externally reachable instances. The source says privileged system-level access is needed to obtain machine keys, so exploitation depends on prior key compromise or related server compromise.
Exploitation context
Active exploitation is supported by the CISA KEV listing. The public bundle does not provide exploit details, observed campaign information, or indicators. The attack path described requires compromised ASP.NET machine keys, making validation of server version and compromise evidence important.
Researcher notes
Key nuance: ConnectWise frames this as platform-level ASP.NET ViewState behavior, not a ScreenConnect-introduced bug. Exploitability depends on machine-key compromise requiring privileged system-level access. The patch removes ViewState dependency rather than fixing the client.
Mitigation direction
- Upgrade ScreenConnect servers to 2025.4 or later per ConnectWise guidance.
- Prioritize externally reachable ScreenConnect servers running 25.2.3 or earlier.
- Review ConnectWise advisories for any updated vendor instructions.
- Investigate possible machine-key exposure if compromise is suspected.
- Do not treat ScreenConnect Client as directly affected based on this source.
Validation and detection
- Inventory ScreenConnect server versions across owned and hosted environments.
- Confirm no ScreenConnect server remains on 25.2.3 or earlier.
- Verify upgraded servers are on 2025.4 or later.
- Review CISA KEV and ConnectWise bulletins for current guidance.
- Check server logs and privileged access records for compromise signs.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-502: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2025-3935 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.1 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.1HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.connectwise.com/company/trust/security-bulletins/screenconnect-security-patch-2025.4CVE reference
- https://www.connectwise.com/company/trust/advisoriesCVE reference
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-3935CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Deserialization of Untrusted Data
Deserialization of Untrusted Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.