VulnerabilityPublished 8 Mar 2026Updated 10 Mar 2026

CVE-2026-3787: UltraVNC · Uncontrolled Search Path

Affects UltraVNCSource CVE Database V5

Public exploit available · CVSS 7.3 High.

Data as of 27 Oct 2026, 05:11 UTC

CVSS 4.0 base score

7.3High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS: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

Base metrics

Attack Vector: Local
Attack Complexity: High
Attack Requirements: None
Privileges Required: Low
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: High
Vulnerable system availability: High
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 8 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: evidence found.
CVSS exploit maturity: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CVSS vector, the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
UltraVNC	Affected =1.6.4.0	Fixed in–

CPE configurations (1)

cpe:2.3:a:ultravnc:ultravnc:*:*:*:*:*:*:*:*

AI-suggested

Organizations should immediately assess their use of UltraVNC version 1.6.4.0 and consider the following mitigations: 1) Restrict local access to systems running UltraVNC to trusted users only, minimizing the risk of local exploitation. 2) Employ application whitelisting and strict DLL loading policies to prevent unauthorized DLL injection or loading from untrusted directories. 3) Use Windows security features such as AppLocker or Windows Defender Application Control to control which DLLs can be loaded by services. 4) Monitor systems for unusual DLL loading behavior or privilege escalation attempts using endpoint detection and response (EDR) tools. 5) If possible, upgrade to a newer version of UltraVNC that addresses this vulnerability once available or consider alternative remote desktop solutions with active vendor support. 6) Implement strict file system permissions on directories involved in DLL loading to prevent unauthorized file placement. 7) Maintain robust local user account management and auditing to detect suspicious activity. These steps go beyond generic advice by focusing on controlling DLL search paths and limiting local attack vectors.

Description

A weakness has been identified in UltraVNC 1.6.4.0 on Windows. This affects an unknown function in the library cryptbase.dll of the component Windows Service. This manipulation causes uncontrolled search path. The attack requires local access. A high degree of complexity is needed for the attack. The exploitability is reported as difficult. The vendor was contacted early about this disclosure but did not respond in any way.

Impact

If exploited, this vulnerability could allow a local attacker with limited privileges to escalate their privileges or execute arbitrary code with the permissions of the vulnerable Windows Service running UltraVNC. This could lead to unauthorized access to sensitive data, disruption of service, or further compromise of the affected system. Since UltraVNC is commonly used for remote administration, successful exploitation could undermine the security of remote management operations, potentially allowing attackers to gain persistent footholds or move laterally within networks. The high complexity and local access requirement limit the scope of immediate widespread exploitation, but targeted attacks in sensitive environments could have severe consequences. The lack of vendor response and patches increases the risk for organizations relying on this software, as they remain exposed to potential future exploits.

Summary

CVE-2026-3787 identifies a vulnerability in UltraVNC version 1.6.4.0 running on Windows platforms, specifically involving an uncontrolled search path weakness linked to the cryptbase.dll library utilized by a Windows Service component. This vulnerability arises when the service improperly handles the search path for loading DLLs, allowing an attacker with local access to influence which DLL is loaded by placing a malicious DLL in a location that is searched before the legitimate one. The attack complexity is high, requiring local access and advanced skills to exploit, and no user interaction is necessary. The vulnerability affects confidentiality, integrity, and availability due to the potential for privilege escalation or arbitrary code execution within the context of the Windows Service. The CVSS 4.0 score is 7.3 (high), reflecting the difficulty of exploitation but significant impact if successfully exploited. No patches or vendor responses have been provided, and no known exploits are currently active in the wild. The vulnerability is particularly concerning because it involves a core Windows library (cryptbase.dll) and a widely used remote desktop tool, UltraVNC, which is often deployed in enterprise environments for remote administration.

References

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