What is the CVSS score of CVE-2026-21551?

CVE-2026-21551 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-2026-21551?

Unisoc modem chipsets (T8100, T9100, T8200, T8300) deployed in mobile devices and IoT systems are vulnerable to remote denial-of-service attacks that disconnect cellular service without user action.

How to fix or mitigate CVE-2026-21551?

Within 24 hours, identify all devices and systems using affected Unisoc chipsets (T8100, T9100, T8200, T8300) and assess exposure across your mobile device fleet and IoT deployments. Within 7 days, segment network access to modems where feasible, enable enhanced monitoring of modem connectivity events, and prioritize inventory of affected devices. Within 30 days, monitor vendor advisories for patch availability, develop a device replacement strategy prioritizing mission-critical systems, and implement network controls to detect abnormal modem communication patterns.

Unisoc Modem CVE-2026-21551

EUVD-2026-52232 HIGH

Improper Input Validation (CWE-20)

2026-08-03 Unisoc

GHSA-8536-j6w6-4932

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-reachable via cellular protocol with no auth or interaction; impact is purely availability loss on the modem subsystem with no scope change.

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 Unisoc modem firmware affects T8100, T9100, T8200, and T8300 chipsets due to improper input validation in the modem stack. Unauthenticated remote attackers can crash or render the modem unresponsive - severing cellular connectivity on affected devices - without requiring any privileges or user interaction. No public exploit code or CISA KEV listing has been identified at time of analysis, though the network-accessible, zero-complexity attack path represents a meaningful availability risk for devices dependent on continuous cellular communication.

Technical ContextAI

The vulnerability resides in the modem firmware component of Unisoc (Shanghai) Technologies chipsets T8100, T9100, T8200, and T8300, as identified by CPE cpe:2.3:a:unisoc_(shanghai)_technologies_co.,_ltd.:t8100/t9100/t8200/t8300. The modem stack processes baseband protocol data received over cellular radio interfaces (e.g., LTE/5G NR control plane or data plane messages). Improper input validation - the root cause class per the description, though no formal CWE is assigned - means the firmware fails to adequately sanitize or bounds-check incoming packets or protocol fields before processing them. A malformed or crafted cellular message can trigger an unhandled condition causing the modem process to fault or crash. Unisoc chipsets are primarily deployed in budget Android smartphones targeting emerging markets; the T8100/T9100/T8200/T8300 series represent mid-to-budget tier SoC families.

RemediationAI

The primary remediation is to apply the modem firmware patch released by Unisoc, as referenced in their product security bulletin at https://www.unisoc.com/en/support/product-security-bulletin/2084109408382668801. Device OEMs integrating T8100/T9100/T8200/T8300 chipsets must incorporate the updated modem binary into their device firmware and distribute it via OTA update to end users. No specific patched firmware version number was provided in the available data; administrators and device owners should monitor Unisoc's bulletin and OEM-specific security advisories for version confirmation. As a compensating control where a patch cannot be immediately applied, organizations managing fleets of affected devices should consider restricting cellular radio exposure - for example, disabling cellular data and limiting to Wi-Fi-only operation reduces the protocol attack surface, though it does not eliminate the baseband radio exposure entirely. Rogue base station attacks cannot be mitigated at the device level without patching; network-level controls such as deploying only on private LTE networks with known infrastructure can reduce exposure in managed deployments. The trade-off of Wi-Fi-only mode is loss of cellular voice and data capability.