CVE-2025-3935: ConnectWise ScreenConnect Improper Authentication Vulnerability
Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.
Generated by VEDAS. Scores as of 2026-11-01 19:19 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.
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.
Description quoted from the CVE record (assigned by ConnectWise, published 2025-04-25).
Weakness: CWE-502 Deserialization of Untrusted Data
How it can be exploited
Exploitable over the network with high attack complexity needing no privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: no. Technical impact: total.
- On CISA KEV since
- 2025-06-02
- US federal deadline
- 2025-06-23
- Ransomware use
- Not known
Public exploit evidence (Exploit Observer)
Also known as: BDU:2025-06256, CNNVD-202504-3733, EUVD-2025-12502, GHSA-qjrp-xr9r-wmrg
VEDAS cluster: VEDAS:FLORALFENNEC
Exploit Observer links 5 pieces of public exploit code or detection modules that name this CVE or one of its aliases.
Exploit code and modules (5)
Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.
- Code repository: https://raw.githubusercontent.com/ARPSyndicate/vedas-signatures/main/nuclei/2025/CVE-2025-3935.yaml
- Code repository: https://raw.githubusercontent.com/ARPSyndicate/vedas-signatures/main/nuclei/2025/CVE-2025-3935.yaml
- Code repository: https://raw.githubusercontent.com/ARPSyndicate/vedas-signatures/main/suricata/2025/CVE-2025-3935.rules
- Code repository: https://raw.githubusercontent.com/ARPSyndicate/vedas-signatures/main/suricata/2025/CVE-2025-3935.rules
- Code repository: https://raw.githubusercontent.com/ARPSyndicate/vedas-signatures/main/suricata/2025/CVE-2025-3935.rules
Vulnerability databases and vendor advisories (6)
Catalogue entries, not exploit evidence.
- Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2025-12502
- Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-qjrp-xr9r-wmrg
- Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2025-3935
- Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-3935
- Vulnerability database or vendor advisory: https://www.cnnvd.org.cn/home/globalSearch?keyword=CNNVD-202504-3733
- Vulnerability database or vendor advisory: https://www.tenable.com/cve/CVE-2025-3935
67 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.
VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.
Live scores
- EPSS
- 0.036
some chance of attack soon - VEDAS
- 0.984
strong exploit evidence - On CISA KEV
- Yes, since 2025-06-02
Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish. The vertical line is the day CISA added it to its exploited list.
Who is affected
| Product | Affected | Not affected |
|---|---|---|
| ConnectWise ScreenConnect | version <25.2.3 | Not stated |
Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.
Exploit Observer also maps it to: connectwise screenconnect, connectwise,_llc. connectwise_screenconnect.
How to fix it
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.
Vendor guidance:
- https://www.connectwise.com/company/trust/security-bulletins/screenconnect-security-patch-2025.4
- https://nvd.nist.gov/vuln/detail/CVE-2025-3935
How to detect it
Nuclei template (active check)
ScreenConnect - Authentication Bypass
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.
Name and description quoted from the template, written by VEDAS.
The template sends 1 request (GET /index.php?x=%22.phpinfo().%22); it decides using status, word matchers. Severity in the template: high. Marked as not yet verified against a live vulnerable target.
Run it against a host you own or are authorised to test:
nuclei -u https://your-host -t CVE-2025-3935.yamlShow the template (37 lines)
id: CVE-2025-3935
info:
name: "ScreenConnect - Authentication Bypass"
author: vedas-arpsyndicate
severity: high
description: |
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.
reference:
- https://www.exploit.observer/?keyword=CVE-2025-3935&match=exact
- https://subdomain.center/?engine=ammonites&keyword=screenconnect&match=exact
classification:
cvss-score: 7.2
cve-id: CVE-2025-3935
cwe-id: CWE-287
metadata:
verified: false
max-request: 1
tags: cve,cve2025,screenconnect,phpinfo
http:
- method: GET
path:
- "{{BaseURL}}/index.php?x=%22.phpinfo().%22"
matchers-condition: and
matchers:
- type: word
part: body
words:
- "<title>phpinfo()"
- "PHP Version"
condition: or
- type: status
status:
- 200
Suricata rules (network detection)
1 rule that alert on traffic matching this exploit: VEDAS CVE-2025-3935 ScreenConnect - Authentication Bypass. Add them to your Suricata rule set and reload.
Show the rules
alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2025-3935 ScreenConnect - Authentication Bypass"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"index.php"; nocase; fast_pattern; content:"phpinfo"; nocase; classtype:web-application-attack; reference:cve,CVE-2025-3935; reference:url,https://www.exploit.observer/?keyword=CVE-2025-3935&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=screenconnect&match=exact; sid:1003814; rev:2;)
References
Government sources
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-3935 (government-resource)
Other references
- https://www.connectwise.com/company/trust/security-bulletins/screenconnect-security-patch-2025.4
- https://www.connectwise.com/company/trust/advisories
Other databases
Where this comes from
This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.