CVE-2026-3787Public exploit

Local code execution via untrusted DLL loading

Published Mar 8, 2026 · Updated Mar 8, 2026

Untrusted DLL loading in the Windows Service in UltraVNC 1.6.4.0 allows local users to execute code via a planted cryptbase.dll. The service searches its application directory for cryptbase.dll and loads an attacker-supplied copy instead of the trusted system library. Reachability requires write access to the installation directory, which normally requires local Administrator rights or explicit ACL grants.

CVSS severity7.0
High
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Untrusted DLL loading in the Windows Service in UltraVNC 1.6.4.0 allows local users to execute code via a planted cryptbase.dll. The service searches its application directory for cryptbase.dll and loads an attacker-supplied copy instead of the trusted system library. Reachability requires write access to the installation directory, which normally requires local Administrator rights or explicit ACL grants.

The record

CVE
CVE-2026-3787
Published
Mar 8, 2026
Updated
Mar 8, 2026
Vendor
UltraVNC Team
Product
UltraVNC
Classifications
CWE-427, CWE-426, T1574.001
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Mar 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.6.4.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

UltraVNC Team · UltraVNCversion=1.6.4.0

Published CVSS scores

7.0VulDBCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
6.0VulDBAV:L/AC:H/Au:S/C:C/I:C/A:C
6.4VulDBCVSS:4.0/AV:L/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-427Uncontrolled Search Path Element
CWE-426Untrusted Search Path
T1574.001DLL Search Order Hijacking

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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