CVE-2025-3935: ConnectWise ScreenConnect Improper Authentication Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run ConnectWise ScreenConnect. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-06-02, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-06-23; treat that as the outer limit, not the target.
• EPSS 3.5%, percentile 89: FIRST’s model estimates a 3.5% chance of exploitation activity in the next 30 days, higher than 89% of all scored CVEs (elevated). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

What it 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.

CISA’s summary

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.

Weakness type: CWE-502, CWE-287.

Product: ConnectWise ScreenConnect · Assigned by: ConnectWise · Published: 2025-04-25

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: high (needs special conditions)
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2025-06-02; federal due date 2025-06-23. Known ransomware use: Unknown.
• CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
• CISA SSVC assessment: exploitation active, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 3.54% probability of exploitation activity in the next 30 days; percentile 89.

Timeline

• 2025-04-25 — CVE record published by ConnectWise
• 2025-06-02 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-06-23 — CISA remediation deadline for US federal agencies
• 2026-02-26 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Listed in CISA KEV notes (connectwise.com) connectwise.com

Vulnerability records

1. CVE.org record CVE-2025-3935 cve.org
2. NVD entry CVE-2025-3935 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

Other references from the CVE record and advisory

1. connectwise.com connectwise.com

All exploited ConnectWise vulnerabilities · Today’s Security Digest