UltraVNC vncWc2Mb calls wcslen() before validating that the wide string is NUL-terminated

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Summary

CVECVE-2026-44041
StatePUBLISHED
Assignersecurin
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-01 05:16:21 UTC
Updated2026-07-02 14:59:32 UTC
DescriptionUltraVNC through 1.8.2.2 contains an out-of-bounds read in the wide-string to multibyte conversion helper. In rfb/dh.cpp:204, the vncWc2Mb() function passes a caller-supplied WCHAR pointer to wcslen() before any bounds check. If the caller provides a wide-character buffer that is not properly NUL-terminated, wcslen() reads past the end of the buffer until it encounters a NUL wchar, resulting in an out-of-bounds read. Under typical Win32 API usage this requires an abnormal caller contract. Impact is limited to a potential information disclosure from adjacent memory regions or a process crash (denial of service) if the over-read crosses a page boundary.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L

EPSS: 0.002840000 probability, percentile 0.201850000 (date 2026-07-02)

Problem Types: CWE-125 | CWE-125 Out-of-bounds Read

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
3.133c584b5-0579-4c06-b2a0-8d8329fcab9cSecondary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
3.1CNACVSS4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Uvnc Ultravnc All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Uvnc UltraVNC affected 1.8.2.2 custom Not specified

References

ReferenceSourceLinkTags
uvnc.com 33c584b5-0579-4c06-b2a0-8d8329fcab9c uvnc.com Product, Release Notes
github.com/ultravnc/UltraVNC 33c584b5-0579-4c06-b2a0-8d8329fcab9c github.com Product
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Arjun Basnet, Securin ([email protected]) (en)

Additional Advisory Data

SourceTimeEvent
CNA2026-06-02T00:00:00.000ZVulnerability discovered during security audit
CNA2026-06-17T00:00:00.000ZReported to vendor (coordinated disclosure)
CNA2026-09-15T00:00:00.000ZPlanned public disclosure (90-day window)
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