CVE-2025-21436: Qualcomm Fastconnect 7800 Race Condition

CVE-2025-21436 is a race condition flaw in Qualcomm Fastconnect 7800 Firmware that causes memory corruption when simultaneous IOCTL calls create processes from different threads. This article covers technical details, impact analysis, affected firmware versions, and recommended mitigation strategies.

CVE-2025-21436 Overview

CVE-2025-21436 is a memory corruption vulnerability affecting a wide range of Qualcomm firmware components. The flaw occurs when two IOCTL calls are initiated simultaneously from separate threads to create processes, resulting in a use-after-free condition [CWE-416]. A local, low-privileged attacker can exploit the race to corrupt kernel memory. Qualcomm addressed the issue in its April 2025 Security Bulletin. Affected components span mobile, wearable, XR, and connectivity chipsets including Snapdragon 8 Gen 3, FastConnect 7800, and multiple WCN, WCD, and WSA series firmware.

Critical Impact
A local attacker with low privileges can trigger memory corruption in kernel context, leading to loss of confidentiality, integrity, and availability on affected Qualcomm-based devices.

Affected Products

Qualcomm Snapdragon 8 Gen 3 Mobile Platform firmware
Qualcomm FastConnect 7800, SM8735, SM8750, SM8750P, QMP1000, SXR2330P firmware
Qualcomm WCN77xx/78xx, WCD93xx, WSA88xx, SW5100(P), and Snapdragon W5+ Gen 1 Wearable Platform firmware

Discovery Timeline

2025-04-07 - CVE-2025-21436 published to NVD
April 2025 - Qualcomm releases fix in the April 2025 Security Bulletin
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-21436

Vulnerability Analysis

The vulnerability is a use-after-free ([CWE-416]) triggered by a race condition between concurrent IOCTL requests. When two threads invoke process-creation IOCTLs at the same time, shared kernel state can be freed by one thread while still referenced by the other. The dangling reference is then used, producing memory corruption in kernel context. Because the attack originates locally through a legitimate driver interface, a low-privileged process on the device can reach the vulnerable code path without user interaction. Successful exploitation can compromise device confidentiality, integrity, and availability, and may enable privilege escalation on the affected Qualcomm platform.

Root Cause

The root cause is missing synchronization around a shared object used during process creation inside the driver's IOCTL handler. One thread frees or reallocates the object while a parallel thread continues to dereference the stale pointer. Absent proper locking or reference counting, the second thread operates on freed memory.

Attack Vector

Exploitation requires local access with low privileges and no user interaction. An attacker executes a program that opens the vulnerable device node and issues two ioctl() calls in parallel threads, each requesting process creation. Repeated execution increases the probability of winning the race and corrupting memory reachable by the driver.

No public proof-of-concept is available. See the Qualcomm April 2025 Security Bulletin for vendor technical details.

Detection Methods for CVE-2025-21436

Indicators of Compromise

Unexpected kernel panics, driver faults, or reboots on Qualcomm-based devices referencing process-creation IOCTL handlers.
Presence of unsigned or unknown user-space binaries repeatedly invoking device-node ioctl() calls with high thread concurrency.
Crash logs showing use-after-free signatures in Qualcomm driver stack frames.

Detection Strategies

Monitor device crash dumps and logcat/kernel logs for repeated faults tied to Qualcomm driver modules and IOCTL entry points.
Baseline legitimate applications that access Qualcomm device nodes and alert on unauthorized processes issuing IOCTLs.
Correlate rapid successive process-creation attempts with concurrent thread activity on the same device handle.

Monitoring Recommendations

Enroll devices in a mobile threat defense or EDR solution that surfaces kernel crash telemetry and anomalous IOCTL usage.
Ingest device logs into a central data lake and build detections for driver fault patterns tied to CVE-2025-21436.
Track firmware and patch-level compliance across the fleet to confirm the April 2025 Qualcomm patch is deployed.

How to Mitigate CVE-2025-21436

Immediate Actions Required

Apply the vendor firmware update from the April 2025 Qualcomm Security Bulletin as soon as OEM builds are available.
Inventory devices using affected Snapdragon, FastConnect, WCN, WCD, WSA, and wearable platforms and prioritize patching.
Restrict installation of untrusted applications that could execute local code on affected devices.

Patch Information

Qualcomm released fixes across the affected firmware families in the Qualcomm April 2025 Security Bulletin. OEMs must integrate the patched firmware into their device updates. Confirm the applicable security patch level with your device manufacturer before considering the issue remediated.

Workarounds

No official workaround exists. Follow the vendor advisory for the authoritative fix.
Reduce local attack surface by enforcing application allow-listing and blocking sideloaded packages on managed devices.
Where feasible, isolate high-value devices from untrusted user-space workloads until firmware updates are applied.