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

> An authenticated administrator can trigger an out-of-bounds write in the rule parser to achieve code execution on the UltraVNC repeater host.

- **Severity:** High 7.2 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Jul 2026
- **Updated:** 9 Jul 2026
- **Also known as:** GHSA-fxj2-5q9g-wmp9

## What is CVE-2026-7829?

CVE-2026-7829 is a high-severity memory corruption vulnerability in uvnc UltraVNC, published on 1 Jul 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official 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.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-7829?

It affects 1 product.


Products: Uvnc Ultravnc.

## How do I fix CVE-2026-7829?

No fix has been published for CVE-2026-7829 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-7829 being exploited?

There is no known exploitation of CVE-2026-7829 in the wild and no public exploit code.

## Other vulnerabilities in uvnc UltraVNC

- [CVE-2019-8264](https://insights.sbomify.com/CVE-2019-8264/): Memory corruption in UltraVNC (critical 9.8)
- [CVE-2019-8265](https://insights.sbomify.com/CVE-2019-8265/): Memory corruption in UltraVNC (critical 9.8)
- [CVE-2019-8266](https://insights.sbomify.com/CVE-2019-8266/): Memory corruption in UltraVNC (critical 9.8)
- [CVE-2019-8280](https://insights.sbomify.com/CVE-2019-8280/): Memory corruption in UltraVNC (critical 9.8)
- [CVE-2018-15361](https://insights.sbomify.com/CVE-2018-15361/): Memory corruption in UltraVNC (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-7829 and fix it if it is affected.

What it is: CVE-2026-7829 is a high-severity memory corruption vulnerability in uvnc UltraVNC, published on 1 Jul 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-7829 in the wild and no public exploit code.

Affected product: uvnc UltraVNC. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-7829/ (Markdown: https://insights.sbomify.com/CVE-2026-7829/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-7829
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-7829
- OSV: https://osv.dev/vulnerability/CVE-2026-7829

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-7829/
Summaries are generated and may contain mistakes; the official description above is the record.