CVE-2025-21439: Qualcomm Fastconnect 6700 Buffer Overflow

CVE-2025-21439 Overview

CVE-2025-21439 is an out-of-bounds write vulnerability [CWE-787] in Qualcomm WLAN drivers. Memory corruption occurs when the driver reads board data through an IOCTL call and copies content to a user-provided output buffer. The flaw affects a broad set of Qualcomm chipsets, including FastConnect 6700/6900, QCM/QCS 5430/6490, QCN7605/7606, WCD9370/9375/9380/9385, and multiple Snapdragon 8c/8cx compute platforms.

A local, low-privileged attacker can trigger the corruption to escalate privileges or destabilize the affected device. Qualcomm addressed the issue in the April 2025 security bulletin.

Critical Impact
Local attackers with low privileges can corrupt kernel memory through the WLAN driver IOCTL interface, potentially achieving code execution at the driver privilege level with high impact to confidentiality, integrity, and availability.

Affected Products

Qualcomm FastConnect 6700 and 6900 firmware
Qualcomm QCM5430, QCM6490, QCS5430, QCS6490, QCA6595AU, QCN7605, QCN7606 firmware
Qualcomm Snapdragon 8c / 8cx / 8cx Gen 2 5G Compute Platforms (SC8180X variants) and WCD9370/9375/9380/9385 audio codec firmware

Discovery Timeline

2025-04-07 - CVE-2025-21439 published to NVD
April 2025 - Qualcomm publishes fix in the April 2025 Security Bulletin
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-21439

Vulnerability Analysis

The vulnerability resides in the Qualcomm WLAN host driver's IOCTL handler that returns board data to userspace. When servicing the request, the driver copies board data content into an output buffer supplied by the caller without correctly validating buffer size against the source length. The mismatch causes an out-of-bounds write, categorized under [CWE-787].

Because the WLAN driver runs in kernel context, corruption of adjacent kernel structures can lead to arbitrary write primitives. Successful exploitation results in loss of confidentiality, integrity, and availability at the operating system level.

Root Cause

The root cause is missing or incorrect bounds enforcement on the destination buffer during the board-data copy path in the WLAN IOCTL handler. The driver trusts a length or offset value tied to the board data blob and writes past the caller-provided output buffer boundary. This class of defect commonly arises when internal blob metadata is used to size a copy without cross-checking the userspace-supplied buffer capacity.

Attack Vector

Exploitation requires local access with low privileges and no user interaction. An attacker executes code on the target device — for example, through a compromised application on an Android handset or a Windows-on-Snapdragon compute platform — and issues a crafted IOCTL to the WLAN driver interface. The driver then performs the vulnerable copy, corrupting kernel memory. No network access is required, but the attack surface is broadly reachable by any process that can open the WLAN device node.

See the Qualcomm Security Bulletin April 2025 for vendor technical details.

Detection Methods for CVE-2025-21439

Indicators of Compromise

Unexpected WLAN driver crashes, kernel panics, or wlan subsystem restarts recorded in dmesg or vendor logs
Non-system processes opening WLAN device nodes (for example /dev/wlan or vendor-specific IOCTL nodes) and issuing atypical ioctl() sequences
Bugreport or crash dumps referencing the board-data read path within the Qualcomm WLAN host driver

Detection Strategies

Monitor endpoint telemetry for local privilege escalation patterns following unusual IOCTL activity from unprivileged processes to WLAN drivers
Correlate application sandbox escapes with subsequent kernel instability on affected Snapdragon-based devices
Track firmware and driver version reporting across the fleet to identify unpatched devices matching the affected CPE list

Monitoring Recommendations

Enable and centralize kernel crash logs from mobile device management (MDM) and Windows-on-ARM endpoints
Alert on repeated WLAN driver faults from the same process or user session, which may indicate exploitation attempts
Baseline expected IOCTL callers to the WLAN interface and flag deviations from that baseline

How to Mitigate CVE-2025-21439

Immediate Actions Required

Apply the Qualcomm April 2025 security patch on all affected chipsets through the OEM update channel as soon as it is available
Inventory devices against the affected CPE list and prioritize models exposed to untrusted third-party applications
Restrict installation of untrusted applications on affected devices until patches are deployed

Patch Information

Qualcomm released fixes in the April 2025 Security Bulletin. Because Qualcomm delivers patches to OEMs, end-user devices receive the fix through vendor firmware or OS updates. Verify the security patch level on Android devices (April 2025 or later) and check OEM update advisories for Snapdragon compute platforms and IoT devices.

Workarounds

No vendor-provided workaround exists; the fix requires the updated firmware or driver from the device OEM
Reduce risk by enforcing application allowlisting and blocking sideloaded applications on managed mobile and compute devices
Where feasible on non-Wi-Fi-dependent devices, disable the WLAN subsystem to remove the exposed IOCTL surface until patched

bash

# Verify Android security patch level (must be 2025-04-05 or later)
adb shell getprop ro.build.version.security_patch

# Enumerate processes with the WLAN device node open to identify unexpected callers
adb shell lsof | grep -i wlan