# CVE-2026-44988: LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes

> A malicious VNC server can trigger out-of-bounds writes in LibVNCClient via crafted Tight encoding rectangles, potentially leading to code execution on the client.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 27 May 2026
- **Updated:** 29 May 2026
- **Also known as:** DEBIAN-CVE-2026-44988, GHSA-jcc5-8wj4-7c58, OESA-2026-2490, OESA-2026-2491, OESA-2026-2564, OESA-2026-2565, SUSE-SU-2026:22190-1, SUSE-SU-2026:2227-1, SUSE-SU-2026:2427-1, SUSE-SU-2026:2428-1, UBUNTU-CVE-2026-44988, openSUSE-SU-2026:10905-1, openSUSE-SU-2026:21118-1

## What is CVE-2026-44988?

CVE-2026-44988 is a high-severity memory corruption vulnerability in libvncserver, published on 27 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient's Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1.

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

## Which versions are affected by CVE-2026-44988?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `LibVNCServer` | SUSE:Linux Enterprise Module for Package Hub 15 SP7 | All versions | 0.9.14-150600.3.9.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server 12 SP5-LTSS | All versions | 0.9.9-17.47.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server 16.0 | All versions | 0.9.14-160000.5.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | All versions | 0.9.9-17.47.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 0.9.14-160000.5.1 |
| `LibVNCServer` | SUSE:Linux Enterprise Workstation Extension 15 SP7 | All versions | 0.9.14-150600.3.9.1 |
| `LibVNCServer` | openSUSE:Leap 16.0 | All versions | 0.9.14-160000.5.1 |
| `LibVNCServer` | openSUSE:Tumbleweed | All versions | 0.9.15-3.1 |

## How do I fix CVE-2026-44988?

Apply the vendor's patch.

## Is CVE-2026-44988 being exploited?

There is no known exploitation of CVE-2026-44988 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44988 and fix it if it is affected.

What it is: CVE-2026-44988 is a high-severity memory corruption vulnerability in libvncserver, published on 27 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-44988 in the wild and no public exploit code.

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-2026-44988/ (Markdown: https://insights.sbomify.com/CVE-2026-44988/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44988
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44988
- OSV: https://osv.dev/vulnerability/CVE-2026-44988

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44988/
Summaries are generated and may contain mistakes; the official description above is the record.