# CVE-2026-20556: MediaTek Modem out-of-bounds write due to missing bounds check

Source: https://junglewise.ai/threats/cve-2026-20556-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-2026-20556 · Severity: info · Published 2026-11-02

A vulnerability in MediaTek's modem firmware allows remote code execution when a device connects to an attacker-controlled cellular base station. An attacker can exploit this to gain system-level privilege escalation on a smartphone or connected device without needing the user to interact or the attacker to have existing access. This could allow complete compromise of the device including data theft and malware installation.

Technologies: [MediaTek Modem](https://junglewise.ai/threats/technologies/modem). Vendors: [MediaTek](https://junglewise.ai/threats/vendors/mediatek).

## Quick answers

**Is CVE-2026-20556 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20556 being exploited in the wild.

**How severe is CVE-2026-20556?** Informational severity, published 2 November 2026.

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

**Is there a fix for CVE-2026-20556?** 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-2026-20556 attacked?** It is attacked over the network or from the adjacent network, in device firmware.

**Am I affected by CVE-2026-20556?** Check whether you run MediaTek Modem. 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 the MediaTek modem due to missing bounds checking. The attack is triggered over-the-air by a rogue base station that the user equipment connects to; no additional privileges or user interaction are required. Successful exploitation results in remote escalation of privilege, granting the attacker kernel-level control of the modem and potentially the host device.

## Affected products

- MediaTek Modem

## 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 privilege escalation via permissions bypass](https://junglewise.ai/threats/cve-2026-68591-in-modem-there-is-a-possible-escalation-of-privilege-due-to-a)
- [MediaTek Modem out-of-bounds write privilege escalation](https://junglewise.ai/threats/cve-2026-68589-in-modem-there-is-a-possible-out-of-bounds-write-due-to-a-missing)
- [MediaTek Modem integer overflow denial of service](https://junglewise.ai/threats/cve-2026-68588-in-modem-there-is-a-possible-way-for-xxx-to-xxxxx-due-to-an)
- [MediaTek Modem logic error denial of service](https://junglewise.ai/threats/cve-2026-20600-in-modem-there-is-a-possible-application-crash-due-to-a-logic)
- [MediaTek Modem privilege escalation due to missing permission check](https://junglewise.ai/threats/cve-2026-20599-in-modem-there-is-a-possible-escalation-of-privilege-due-to-a)