# CVE-2026-20557: MediaTek Modem out of bounds write due to missing bounds check

Source: https://junglewise.ai/threats/cve-2026-20557-in-modem-there-is-a-possible-out-of-bounds-write-due-to-a-missing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-02. Updated: 2026-11-02  
License: CC BY 4.0 with a link back

CVE-2026-20557 · Severity: info · Published 2026-11-02

MediaTek modems are chipsets that handle cellular connectivity in smartphones and IoT devices. A missing bounds check in modem firmware can allow an attacker controlling a rogue base station to remotely gain elevated privileges on a device connected to that station. An attacker could exploit this to take complete control of the device and access sensitive data without any user interaction.

Vendors: [MediaTek](https://junglewise.ai/threats/vendors/mediatek).

## Quick answers

**Is CVE-2026-20557 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20557 being exploited in the wild.

**How severe is CVE-2026-20557?** Informational severity, published 2 November 2026.

**Which products and versions are affected?** MediaTek Modem firmware.

**Is there a fix for CVE-2026-20557?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-20557 attacked?** It is attacked over the network or from the adjacent network, in device firmware.

**Am I affected by CVE-2026-20557?** Check whether you run MediaTek Modem firmware. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An out of bounds write vulnerability exists in MediaTek modem firmware due to insufficient bounds checking. The vulnerability can be triggered remotely when a user equipment (UE) connects to a rogue base station controlled by an attacker, requiring no additional privileges. Successful exploitation results in privilege escalation on the affected device.

## Affected products

- MediaTek Modem firmware

## Timeline

- 2026-11-02: disclosed

## References

- [https://www.mediatek.com/product-security-bulletin/November-2026](https://www.mediatek.com/product-security-bulletin/November-2026)

## Related threats

- [MediaTek Modem out-of-bounds read with missing bounds check](https://junglewise.ai/threats/cve-2026-20594-in-modem-there-is-a-possible-out-of-bounds-read-due-to-a-missing)