CVE-2025-3935ConnectWise ScreenConnect Improper Authentication Vulnerability
CVE-2025-3935 is a deserialization of untrusted data in ConnectWise ScreenConnect, rated high (7.2 on CVSS 3.1).
Why this priority: Exploited in the wild: listed in CISA's KEV catalog.
Published · Updated · NVD status: Analyzed
What it is
Serialized objects from outside are turned back into live objects, which a crafted payload can abuse to run code.
How it is reached
An attacker can exploit it over the network, with an administrator account, and nobody has to click anything.
What an attacker gains
A successful attack can read the data it protects, change data or behaviour and take it offline. In practice, this kind of flaw lets an attacker turn crafted data into code execution inside the receiving service.
Is it being exploited?
CISA added it to the Known Exploited Vulnerabilities catalog on 2025-06-02: it is being exploited in the wild. EPSS estimates a 3.6% chance of exploitation activity in the next 30 days, higher than 90% of scored CVEs.
What to do
- Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2025-06-23.
- Upgrade ConnectWise ScreenConnect to 25.2.3 or later.
- Until it is patched, review who holds accounts that can reach it.
- Check exposed instances for signs of compromise, not only for the version.
Description from NVD
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.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- APIs, queues and caches that accept serialized objects. The flaw sits between a message producer and the service that deserializes it.
Trust boundaries in play
- Authenticated network access. An account is needed, so exposure follows who can sign in: customers, partners or staff.
- Between a message producer and the service that deserializes it. An attacker who crosses it can turn crafted data into code execution inside the receiving service.
Questions to answer about your own systems
- Where does ConnectWise ScreenConnect run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.