CVE-2026-21370: Qualcomm Fastconnect Buffer Overflow Flaw

CVE-2026-21370 Overview

CVE-2026-21370 is a memory corruption vulnerability affecting a broad range of Qualcomm firmware, including Snapdragon mobile platforms, FastConnect wireless subsystems, and automotive SoCs. The flaw occurs during validation of input batch size when the buffer plane count exceeds maximum allowed values, resulting in an out-of-bounds write condition [CWE-787]. An authenticated local attacker with low privileges can trigger the corruption without user interaction. Qualcomm disclosed the issue in the July 2026 Security Bulletin and assigned it a CVSS 3.1 score of 5.3 (Medium).

Critical Impact
Local attackers with low privileges can trigger out-of-bounds memory writes in Qualcomm firmware, potentially degrading device integrity, confidentiality, and availability across mobile, automotive, and IoT platforms.

Affected Products

Qualcomm Snapdragon mobile platforms (Snapdragon 8 Elite, 8 Gen 1/2, 8+ Gen 2, 7 Gen 1, 6 Gen 1/3, 4 Gen 2, 460, 662, AR1 Gen 1, XR2 5G, XR2+ Gen 1)
Qualcomm FastConnect (6700, 6900, 7800), WCN/WCD/WSA audio and connectivity firmware, and QCA chipsets
Qualcomm automotive and compute platforms (SA8255P, SA8620P, SA8770P, SA9000P, QCS8550, QCM4490, X1E80100)

Discovery Timeline

2026-07-06 - CVE-2026-21370 published to NVD
2026-07-07 - Last updated in NVD database
July 2026 - Qualcomm publishes fix in the July 2026 Security Bulletin

Technical Details for CVE-2026-21370

Vulnerability Analysis

The vulnerability resides in firmware routines that process buffer descriptors containing multi-plane image or media data. When the code validates the input batch size, it fails to correctly enforce the maximum allowed buffer plane count. When the plane count exceeds the defined maximum, downstream logic writes beyond the bounds of the allocated buffer structure, corrupting adjacent memory.

Because the flaw exists in firmware handling structured client input, exploitation requires local access to the interface that submits batches to the affected component. Successful triggering leads to memory corruption that can influence firmware state, cause instability, or serve as a primitive in a larger exploit chain against the baseband, connectivity, or media subsystem.

Root Cause

The root cause is an improper input validation defect classified under [CWE-787] Out-of-bounds Write. The validation logic checks the batch size but does not properly gate the plane count against the maximum supported value before the plane array is dereferenced or iterated. This allows attacker-controlled metadata to drive writes past the destination buffer.

Attack Vector

The attack vector is Local (AV:L) with Low privileges required (PR:L) and no user interaction (UI:N). An attacker with code execution in a low-privileged process on the device — for example, a compromised application or service capable of interacting with the affected firmware interface — supplies a crafted request specifying a plane count greater than the enforced maximum. The firmware then performs the out-of-bounds write. Remote exploitation over the network is not indicated by the CVSS vector.

No public proof-of-concept, exploit code, or evidence of exploitation in the wild has been published. The EPSS probability is 0.06%, reflecting a low near-term exploitation likelihood.

Detection Methods for CVE-2026-21370

Indicators of Compromise

Unexpected firmware crashes, subsystem restarts, or SSR (subsystem restart) events involving connectivity, audio, or media firmware on affected Qualcomm SoCs
Kernel or HAL log entries referencing invalid plane counts, malformed buffer descriptors, or batch validation failures
Anomalous local processes issuing high-frequency or malformed ioctl/binder requests to Qualcomm media, camera, or connectivity drivers

Detection Strategies

Monitor device telemetry for repeated firmware faults, watchdog resets, or crash dumps correlated with the affected subsystems
Baseline legitimate application access to Qualcomm HAL interfaces and alert on unauthorized or unexpected callers
Correlate mobile device management (MDM) inventory with the Qualcomm July 2026 patch level to identify unpatched endpoints

Monitoring Recommendations

Ingest mobile and IoT device logs into a centralized analytics platform to detect firmware anomalies at scale
Track patch adoption rates for the July 2026 Qualcomm Security Bulletin across fleet devices
Watch OEM security bulletins (Google Android, Samsung, automotive OEMs) for downstream advisories referencing CVE-2026-21370

How to Mitigate CVE-2026-21370

Immediate Actions Required

Apply the firmware updates referenced in the Qualcomm July 2026 Security Bulletin as soon as OEM builds become available
Inventory all devices using affected Snapdragon, FastConnect, WCN/WCD/WSA, QCA, and automotive Qualcomm components
Restrict installation of untrusted applications on affected mobile and embedded devices to reduce local attack surface

Patch Information

Qualcomm addressed CVE-2026-21370 in updates published with the Qualcomm July 2026 Security Bulletin. Fixes are delivered to OEMs and integrated into device-specific firmware and Android security patch level (SPL) releases. Consult the applicable OEM (Google, Samsung, Xiaomi, automotive vendors, etc.) for the specific build containing the fix for each affected platform.

Workarounds

No official workaround has been published by Qualcomm; patching remains the authoritative remediation
Enforce least-privilege application policies and app-store vetting to limit which local processes can reach affected firmware interfaces
For managed fleets, use MDM policies to block sideloading and constrain access to sensitive HAL surfaces until patches are deployed