UltraVNC repeater authenticated out-of-bounds write in rule parser via oversized token

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Summary

CVECVE-2026-7829
StatePUBLISHED
Assignersecurin
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-01 05:16:24 UTC
Updated2026-07-02 15:09:54 UTC
DescriptionUltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the allow/deny rule parser. In repeater/webgui/settings.c:225-272, after strncpy_s copies a rule token into temp1[rule1] (25-byte destination) or temp2/temp3 (16-byte destination), the code unconditionally writes a NUL terminator at temp1[rule1][len] = 0 without clamping len to the destination size. When an authenticated administrator saves a rule with a token length equal to or greater than the destination size, the NUL byte is written one or more bytes past the end of the stack-allocated array, corrupting adjacent stack data. An attacker who has obtained admin credentials (including via CVE-2026-7839 default password) can trigger this to gain code execution on the repeater host.

Risk And Classification

Primary CVSS: v3.1 7.2 HIGH from 33c584b5-0579-4c06-b2a0-8d8329fcab9c

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

EPSS: 0.005040000 probability, percentile 0.394000000 (date 2026-07-02)

Problem Types: CWE-787 | CWE-787 Out-of-bounds Write

VersionSourceTypeScoreSeverityVector
3.133c584b5-0579-4c06-b2a0-8d8329fcab9cSecondary7.2HIGHCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
3.1CNACVSS7.2HIGHCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

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

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

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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