CVE-2026-1679: Zephyr Buffer Overflow Vulnerability

CVE-2026-1679 Overview

A buffer overflow vulnerability exists in the Zephyr RTOS eswifi socket offload driver that allows local attackers to corrupt kernel memory. The driver copies user-provided payloads into the fixed eswifi->buf buffer without verifying that adequate space is available, enabling oversized socket send operations to overflow the buffer boundary and corrupt adjacent kernel memory regions (CWE-120).

Critical Impact

Local code execution through kernel memory corruption via the socket send API, potentially leading to complete system compromise on affected IoT and embedded devices.

Affected Products

• Zephyrproject Zephyr RTOS (all versions prior to patch)
• Devices using the eswifi WiFi socket offload driver
• Embedded systems and IoT devices built on Zephyr RTOS

Discovery Timeline

• 2026-03-28 - CVE-2026-1679 published to NVD
• 2026-03-31 - Last updated in NVD database

Technical Details for CVE-2026-1679

Vulnerability Analysis

This buffer overflow vulnerability (CWE-120: Buffer Copy without Checking Size of Input) resides in the eswifi socket offload driver, a component responsible for handling WiFi socket operations in Zephyr RTOS. The fundamental flaw lies in the driver's failure to validate the size of user-supplied data before copying it into the statically-sized eswifi->buf buffer.

When applications invoke the socket send API with payload data, the eswifi driver should verify that the incoming data fits within the allocated buffer space. However, the vulnerable code path bypasses this critical bounds check, directly copying the payload regardless of size constraints. This allows an attacker with local code execution capabilities to craft oversized payloads that exceed the buffer capacity, resulting in a classic stack or heap buffer overflow depending on where eswifi->buf is allocated.

The impact includes potential arbitrary code execution at the kernel level, denial of service through kernel panic, and corruption of sensitive kernel data structures that could be leveraged for privilege escalation within the embedded system.

Root Cause

The root cause is a missing bounds check in the eswifi socket offload driver. The driver accepts user-provided payload data through the socket send API and copies it directly into the fixed-size eswifi->buf buffer without first comparing the payload length against the buffer's capacity. This violation of secure coding practices allows buffer overflow conditions to occur when the application supplies data exceeding the buffer's size.

Attack Vector

Exploitation requires local code execution on the target Zephyr-based device with the ability to call socket API functions. An attacker would need to:

1. Gain the ability to execute code on the embedded device (through a compromised application, malicious firmware update, or other initial access vector)
2. Open a socket using the eswifi driver
3. Invoke the socket send function with a crafted payload larger than the eswifi->buf buffer capacity
4. The overflow corrupts adjacent kernel memory, potentially allowing arbitrary write primitives

While direct remote exploitation is not possible, this vulnerability significantly amplifies the impact of any initial code execution foothold on affected devices.

The vulnerability mechanism involves the socket send operation directly copying user data into eswifi->buf without size validation. When oversized payloads are passed, memory beyond the buffer boundary is overwritten. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-1679

Indicators of Compromise

• Unexpected system crashes or kernel panics on Zephyr-based devices
• Anomalous socket send operations with unusually large payload sizes in application logs
• Memory corruption signatures in crash dumps indicating buffer overflow patterns
• Unusual behavior in applications utilizing the eswifi WiFi driver

Detection Strategies

• Monitor for applications making socket send calls with payload sizes exceeding expected limits
• Implement runtime memory protection mechanisms to detect buffer overflow attempts
• Deploy crash analysis tools to identify overflow patterns in kernel memory dumps
• Review application code for socket API usage patterns that could trigger the vulnerability

Monitoring Recommendations

• Enable kernel debugging and crash dump collection on development and test devices
• Implement logging for socket operations through the eswifi driver where feasible
• Monitor for firmware integrity changes that could indicate exploitation attempts
• Establish baselines for normal socket operation patterns on production devices

How to Mitigate CVE-2026-1679

Immediate Actions Required

• Review and update Zephyr RTOS to the latest patched version addressing this vulnerability
• Audit all applications using the eswifi socket driver for potential exposure
• Implement application-level input validation on socket send operations as a defense-in-depth measure
• Isolate affected devices from untrusted code execution paths where possible

Patch Information

Zephyrproject has released a security advisory addressing this vulnerability. Organizations using Zephyr RTOS with the eswifi socket offload driver should consult the GitHub Security Advisory GHSA-qx3g-5g22-fq5w for specific patch information and updated firmware versions.

Workarounds

• Implement application-layer bounds checking on all data passed to socket send operations
• Limit the maximum payload size at the application level before calling socket APIs
• Restrict execution of untrusted code on affected devices to reduce attack surface
• Consider disabling the eswifi driver if not required for device functionality

# Zephyr RTOS configuration example to limit socket buffer sizes
# Add to prj.conf or device configuration
CONFIG_NET_BUF_DATA_SIZE=1500
CONFIG_NET_PKT_RX_COUNT=16
CONFIG_NET_PKT_TX_COUNT=16
# Ensure strict memory bounds checking during development
CONFIG_ASSERT=y
CONFIG_STACK_CANARIES=y