What is the CVSS score of CVE-2026-21552?

CVE-2026-21552 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. EPSS exploitation probability: 0.4%.

Which versions of Unisoc Modem are affected by CVE-2026-21552?

Unisoc modem chipsets (T8100, T9100, T8200, T8300) used across mobile devices and IoT equipment are vulnerable to unauthenticated remote denial-of-service attacks that disable cellular connectivity…

How to fix or mitigate CVE-2026-21552?

Within 24 hours, inventory all devices and infrastructure containing Unisoc T8100, T9100, T8200, or T8300 chipsets across your organization, prioritizing business-critical and mission-essential systems. Within 7 days, implement network monitoring to detect anomalous cellular signaling activity and establish communication failover procedures for affected critical systems. Within 30 days, establish a monitoring protocol for Unisoc security advisories, evaluate patching timelines directly with device vendors, and develop a device replacement strategy for highest-risk deployments where cellular availability is non-negotiable.

Unisoc Modem CVE-2026-21552

EUVD-2026-52233 HIGH

Improper Input Validation (CWE-20)

2026-08-03 Unisoc

GHSA-4c53-w7qg-m85h

Denial Of Service T8100 T9100 T8200 T8300 Unisoc Shanghai Technologies Co Ltd

7.5

CVSS 3.1 · Vendor: Unisoc

Severity by source

Vendor (Unisoc) PRIMARY

7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

vuln.today AI

7.5 HIGH

Network-delivered cellular signaling requires no victim-side privileges or interaction; impact is availability-only with no scope change beyond the modem.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (Unisoc).

CVSS VectorVendor: Unisoc

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Lifecycle Timeline

Analysis Generated

Aug 03, 2026 - 08:23 vuln.today

CVE Published

Aug 03, 2026 - 07:18 cve.org

HIGH 7.5

DescriptionCVE.org

In modem, there is a possible improper input validation. This could lead to remote denial of service with no additional execution privileges needed

AnalysisAI

Remote denial of service in the modem firmware of Unisoc T8100, T9100, T8200, and T8300 chipsets allows an unauthenticated remote attacker to crash the modem subsystem by sending crafted cellular signaling data, disabling cellular connectivity on affected devices. The CVSS 3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) reflects full availability impact with no victim-side prerequisites, though practical exploitation requires the attacker to control or simulate cellular network infrastructure in radio proximity. No public exploit has been identified at time of analysis, and this vulnerability has not been added to the CISA KEV catalog.

Technical ContextAI

The vulnerability resides in the modem firmware of Unisoc T8100, T9100, T8200, and T8300 application processor chipsets, as identified in CPE string cpe:2.3:a:unisoc_(shanghai)_technologies_co.,_ltd.:t8100/t9100/t8200/t8300. These are low-to-mid range SoCs used primarily in budget Android smartphones and tablets sold in emerging markets. The modem subsystem is responsible for processing the cellular protocol stack - including 2G/3G/4G signaling - and inherently receives data from radio network infrastructure before any higher-level authentication occurs. The root cause is improper input validation (CWE not specified by NVD or vendor) in the modem firmware's protocol parser, meaning the firmware fails to adequately check the structure or bounds of incoming signaling messages before processing them. This class of flaw in modem firmware is well-documented across multiple chipset vendors and can be triggered over-the-air without physical access to the device.

RemediationAI

The primary remediation is to apply updated modem firmware from Unisoc as detailed in the product security bulletin at https://www.unisoc.com/en/support/product-security-bulletin/2084109408382668801. Patch available per vendor advisory; however, no exact fixed firmware version number is confirmed from the available data - OEMs should contact Unisoc directly to obtain the patched modem binary and push it to end users via OTA update. Device manufacturers shipping T8100/T9100/T8200/T8300-based products should prioritize integrating and distributing this update given the unauthenticated remote attack path. As a compensating control where patching is not immediately feasible, organizations managing device fleets can restrict cellular roaming to vetted and trusted network operators, which reduces exposure to rogue base station attacks; however, this restricts user mobility and does not eliminate risk on home networks. There are no software-layer workarounds that fully mitigate a modem firmware input validation flaw without the underlying patch.