CVE-2025-21455: Qualcomm Fastconnect Buffer Overflow Flaw

CVE-2025-21455 Overview

CVE-2025-21455 is a memory corruption vulnerability affecting a broad range of Qualcomm chipsets and firmware. The flaw occurs when userspace submits blob data to kernel space through an IOCTL interface. Qualcomm disclosed the issue in the August 2025 security bulletin. The underlying weakness is classified as [CWE-367] Time-of-Check Time-of-Use (TOCTOU), where the kernel validates buffer state at one point but operates on it later, allowing a local attacker to corrupt kernel memory. Successful exploitation impacts confidentiality, integrity, and availability of affected devices, and can enable local privilege escalation on Snapdragon, FastConnect, and related platforms.

Critical Impact
A local attacker with low privileges can trigger kernel memory corruption through crafted IOCTL calls, leading to potential arbitrary code execution in kernel context on affected Qualcomm chipsets.

Affected Products

Qualcomm Snapdragon 8 Gen 1, Snapdragon 865/865+/870 5G Mobile Platforms
Qualcomm FastConnect 6800, 6900, and 7800 firmware
Qualcomm QCA6391/QCA6426/QCA6436, WCN3980/WCN3988, WSA88xx, WCD9380/WCD9385, SDX55, SXR2130/2230P/2250P, SW5100/SW5100P, and Snapdragon XR2 5G platforms

Discovery Timeline

2025-08-06 - CVE-2025-21455 published to NVD
August 2025 - Qualcomm publishes advisory in the Qualcomm Security Bulletin August 2025
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-21455

Vulnerability Analysis

The vulnerability resides in a kernel IOCTL handler that accepts blob data from userspace. During processing, the driver validates properties of the incoming buffer (such as size or pointer validity) and later re-references the same userspace-controlled data when performing kernel operations. Because the buffer resides in a shared address space, a concurrent thread can modify the data between validation and use. This TOCTOU condition causes the kernel to operate on data that no longer matches the validated state, corrupting kernel memory structures. Given the local, low-privilege attack vector, any process able to open the device node can attempt exploitation.

Root Cause

The root cause is a race condition classified as [CWE-367] Time-of-Check Time-of-Use. The kernel driver reads userspace blob data more than once without copying it into kernel memory before validation completes. An attacker races the validation logic by mutating the buffer contents from another thread, invalidating security assumptions the driver relies on.

Attack Vector

Exploitation requires local code execution on the target device with permission to interact with the vulnerable Qualcomm kernel driver's IOCTL interface. An attacker application spawns two threads: one issues the IOCTL with a crafted blob, and the other continuously rewrites the blob contents in userspace. Winning the race allows the attacker to bypass kernel-side validation and corrupt kernel memory, potentially achieving elevation of privilege to kernel context. No user interaction is required.

No public proof-of-concept has been observed for CVE-2025-21455 at the time of writing, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-21455

Indicators of Compromise

Unexpected kernel panics, oops messages, or reboots on devices using affected Qualcomm chipsets, particularly correlated with third-party application activity.
Kernel logs (dmesg, logcat -b kernel) showing faults inside Qualcomm driver modules handling IOCTL blob submissions.
Unsigned or sideloaded applications repeatedly opening Qualcomm device nodes under /dev/ and issuing high volumes of IOCTL calls.

Detection Strategies

Monitor endpoints for processes performing rapid, repeated IOCTL calls against Qualcomm driver device nodes from unprivileged contexts.
Correlate crash telemetry from mobile fleet management or MDM solutions to identify clusters of kernel faults on unpatched firmware versions.
Inspect installed application behavior for multi-threaded interaction with kernel driver interfaces, which is a hallmark of TOCTOU exploitation attempts.

Monitoring Recommendations

Enroll affected mobile and embedded devices in centralized logging to capture kernel crash reports and driver-level errors.
Track firmware and platform build numbers across the fleet and alert when devices remain on pre-August 2025 Qualcomm patch levels.
Enable application behavior analytics that flag privilege escalation patterns and anomalous system call sequences against hardware drivers.

How to Mitigate CVE-2025-21455

Immediate Actions Required

Apply the vendor firmware updates provided through OEM channels that incorporate Qualcomm's August 2025 patches for affected chipsets.
Inventory devices using the affected FastConnect, QCA, WCN, WSA, WCD, SDX, SXR, SW, and Snapdragon components and prioritize patch rollout for high-value or exposed devices.
Restrict installation of untrusted applications on unpatched devices, since exploitation requires local code execution.

Patch Information

Qualcomm released fixes as part of the Qualcomm Security Bulletin August 2025. Patches are delivered to end users through OEM firmware and Android security updates. Device manufacturers must integrate Qualcomm's updated driver code into their own firmware releases before mitigations reach affected handsets, IoT devices, and XR platforms.

Workarounds

Enforce application allowlisting and Mobile Device Management (MDM) policies that block sideloading on affected devices until firmware updates are deployed.
Reduce device exposure by disabling debug interfaces, developer mode, and USB debugging on production devices.
Where feasible, limit access to Qualcomm driver device nodes through SELinux policy hardening on managed Android builds.

bash

# Example: verify Qualcomm patch level on an Android device
adb shell getprop ro.build.version.security_patch
adb shell getprop ro.vendor.build.security_patch

# Confirm the device is at or beyond the August 2025 patch level
# Expected output: 2025-08-01 or later