CVE-2025-71251: IMS Denial of Service Vulnerability

CVE-2025-71251 Overview

CVE-2025-71251 is an improper input validation vulnerability in the IP Multimedia Subsystem (IMS) component shipped on Unisoc-based devices. A remote attacker can send malformed input to trigger a system crash, resulting in denial of service. No authentication, user interaction, or elevated privileges are required to exploit the flaw.

The vulnerability is reachable over the network and impacts only availability. It does not provide additional code execution or privilege escalation. Unisoc disclosed the issue in its product security bulletin.

Critical Impact

Remote unauthenticated attackers can crash the IMS subsystem on affected Unisoc devices, disrupting voice and multimedia services until the device recovers.

Affected Products

• Unisoc chipset platforms running the affected IMS component
• Mobile devices integrating Unisoc baseband and IMS stack
• Refer to the Unisoc Product Security Bulletin for the complete chipset and version list

Discovery Timeline

• 2026-05-06 - CVE-2025-71251 published to NVD
• 2026-05-07 - Last updated in NVD database

Technical Details for CVE-2025-71251

Vulnerability Analysis

The flaw resides in the IMS implementation used to deliver voice, video, and messaging services over IP. The IMS layer fails to properly validate input received over the network before processing it. Malformed data reaches code paths that assume well-formed structures, leading to an unrecoverable error state and a system crash.

Because the attack vector is network-based and authentication is not required, an adversary on a path that can deliver IMS traffic to the device can repeatedly trigger the condition. The result is a denial of service against telephony and IMS-dependent services. Confidentiality and integrity are not affected, but availability is fully impacted on the targeted device.

Root Cause

The root cause is improper input validation within the IMS message processing logic. Fields or structures parsed from incoming traffic are not bounds-checked or type-validated before use. When an attacker supplies values outside expected ranges or formats, the parser enters an invalid state that the system cannot handle gracefully, causing a crash.

Attack Vector

Exploitation occurs remotely over the network. An attacker delivers a crafted IMS message to a vulnerable device. The malformed input triggers the unhandled error path inside the IMS stack and crashes the subsystem, interrupting calls and IMS services. No public proof-of-concept exploit is currently listed for this CVE.

No verified exploit code is available. See the Unisoc Product Security Bulletin for vendor-supplied technical details.

Detection Methods for CVE-2025-71251

Indicators of Compromise

• Unexpected restarts or crashes of the IMS service or telephony stack on Unisoc-based devices
• Sudden loss of VoLTE, VoWiFi, or RCS functionality without user-initiated changes
• Repeated crash logs referencing IMS message parsing on the device

Detection Strategies

• Monitor mobile device management (MDM) telemetry for IMS or telephony subsystem crash events on Unisoc fleets
• Correlate carrier-side IMS signaling anomalies with device-side service interruptions
• Track abnormal volumes of malformed IMS signaling traffic targeting subscriber endpoints

Monitoring Recommendations

• Enable crash and reliability reporting on managed mobile endpoints to surface repeated IMS failures
• Forward device and carrier logs to a centralized analytics platform for cross-source correlation
• Establish baselines for IMS service availability and alert on deviations

How to Mitigate CVE-2025-71251

Immediate Actions Required

• Inventory devices using affected Unisoc chipsets and IMS firmware versions
• Apply the security update referenced in the Unisoc bulletin as soon as the device OEM publishes it
• Coordinate with carriers to filter malformed IMS signaling at the network edge where feasible

Patch Information

Unisoc has published remediation guidance in the Unisoc Product Security Bulletin. Device OEMs must integrate the Unisoc patch into their firmware images and deliver it through over-the-air updates. End users should install OEM firmware updates promptly once available.

Workarounds

• Disable VoLTE, VoWiFi, or other IMS-dependent features on affected devices if operationally acceptable until a patch is applied
• Restrict device exposure to untrusted IMS networks where possible
• Engage mobile network operators to apply signaling filters that drop malformed IMS messages

# No vendor-supplied configuration mitigation is available.
# Apply OEM firmware updates that incorporate the Unisoc patch.