CVE-2025-3935
CVE-2025-3935 is a security flaw in ConnectWise ScreenConnect, remote-support software IT providers use to manage their customers’ computers. Attackers can run their own code on ConnectWise ScreenConnect. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 2 Jun 2025.[1]
ConnectWise ScreenConnect is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. ConnectWise has published a fix or advice.
Description
CISA calls it an improper authentication in ConnectWise ScreenConnect. In its words: “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.”[1]
The CVE record adds: “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.”[2]
The underlying weakness is improper authentication (CWE-287), in MITRE’s list of common software weaknesses.
It scores 7.2 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; ConnectWise’s advisory has them[3]. CISA names the product as ConnectWise ScreenConnect.
Most families won’t have ConnectWise ScreenConnect; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 2 Jun 2025, 38 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 23 Jun 2025 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 4%. That’s in the top 11% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
ConnectWise has published a fix or advice.[3] CISA’s 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.”[1]
- Check whether you use it.ConnectWise ScreenConnect is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 23 Jun 2025 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.2.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 4%.[4] |
See also
Other ConnectWise ScreenConnect flaws
- CVE-2026-84869: improper privilege management and missing authorization ·
- CVE-2024-1708: path traversal ·
- CVE-2024-1709: authentication bypass ·
Other improper authentication flaws
- CVE-2026-105133, AhsayCBS: improper authentication ·
- CVE-2026-42018, JFrog Artifactory: improper authentication ·
- CVE-2026-82329, JFrog Artifactory: improper authentication ·
- CVE-2026-59822, BerriAI LiteLLM: improper authentication ·
- CVE-2023-49105, ownCloud: improper authentication ·
Added the same day
- CVE-2025-35939, Craft CMS: external control of assumed-immutable web parameter ·
- CVE-2024-56145, Craft CMS: code injection ·
- CVE-2023-39780, ASUS RT-AX55 Routers: OS command injection ·
- CVE-2021-32030, ASUS Routers: improper authentication ·
Every ConnectWise flaw on CISA’s list · Everything added in June 2025
References
- ^ Cybersecurity and Infrastructure Security Agency. “ConnectWise ScreenConnect Improper Authentication Vulnerability”. Known Exploited Vulnerabilities Catalog, added 2 Jun 2025.
- ^ National Institute of Standards and Technology. “CVE-2025-3935 Detail”. National Vulnerability Database, published 25 Apr 2025.
- ^ ConnectWise. Advisories and fixes: connectwise.com, connectwise.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.036, percentile 89.5, 31 Oct 2026.
- CVE Program. “CVE-2025-3935”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.