# CVE-2026-32853: LibVNCServer UltraZip Encoding Heap Out-of-bounds Read

> A malicious VNC server can trigger a heap out-of-bounds read in LibVNCServer, leading to information disclosure or application crashes.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Mar 2026
- **Updated:** 14 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-32853, GHSA-87q7-v983-qwcj, UBUNTU-CVE-2026-32853

## What is CVE-2026-32853?

CVE-2026-32853 is a medium-severity vulnerability in LibVNCServer, published on 24 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

LibVNCServer versions 0.9.15 and prior (fixed in commit 009008e) contain a heap out-of-bounds read vulnerability in the UltraZip encoding handler that allows a malicious VNC server to cause information disclosure or application crash. Attackers can exploit improper bounds checking in the HandleUltraZipBPP() function by manipulating subrectangle header counts to read beyond the allocated heap buffer.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-32853?

It affects 1 product.


Products: Libvncserver Project Libvncserver.

## How do I fix CVE-2026-32853?

Apply the vendor's patch.

## Is CVE-2026-32853 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-32853 exists.

## Other vulnerabilities in LibVNCServer

- [CVE-2016-9941](https://insights.sbomify.com/CVE-2016-9941/): Memory corruption in n/a (critical 9.8)
- [CVE-2016-9942](https://insights.sbomify.com/CVE-2016-9942/): Memory corruption in n/a (critical 9.8)
- [CVE-2026-32854](https://insights.sbomify.com/CVE-2026-32854/): LibVNCServer httpd proxy NULL Pointer Dereference (medium 6.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-32853 and fix it if it is affected.

What it is: CVE-2026-32853 is a medium-severity vulnerability in LibVNCServer, published on 24 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-32853 exists.

Affected product: LibVNCServer. 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-2026-32853/ (Markdown: https://insights.sbomify.com/CVE-2026-32853/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-32853
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-32853
- OSV: https://osv.dev/vulnerability/CVE-2026-32853

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-32853/
Summaries are generated and may contain mistakes; the official description above is the record.