CVE-2026-1681: Network Stack Buffer Overflow Vulnerability

CVE-2026-1681 Overview

CVE-2026-1681 is an uncontrolled recursion vulnerability [CWE-674] in the Zephyr real-time operating system network stack. Issuing an Internet Control Message Protocol (ICMP) ping through the net ping shell command to the device's own IPv4 address triggers a stack overflow on the system work-queue. The stack recognizes the destination as a local address and processes both the echo request and the echo reply inline. Nested input-path frames exceed the available work-queue stack size and corrupt execution state.

Critical Impact

A local operator with shell access can crash the Zephyr device by pinging its own IPv4 address, producing a denial-of-service condition through stack overflow.

Affected Products

• Zephyr Project real-time operating system
• Devices exposing the net ping shell command with IPv4 networking enabled
• Embedded systems using the affected Zephyr network stack input path

Discovery Timeline

• 2026-05-12 - CVE-2026-1681 published to the National Vulnerability Database (NVD)
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-1681

Vulnerability Analysis

The defect resides in the Zephyr IPv4 input processing path invoked from the system work-queue. When a user issues net ping targeting the device's own assigned IPv4 address, the stack short-circuits the normal transmit path and dispatches the packet directly to the local input handler. The handler generates an ICMP echo reply, which is itself recognized as locally destined and re-enters the same input function on the same call stack.

Each recursion level consumes additional work-queue stack space for protocol headers, packet metadata, and local variables. Because the recursion has no terminating condition for the self-addressed case, the call depth grows until the work-queue thread's stack guard is breached. The resulting overflow produces undefined behavior, kernel fault, or a system reset.

Root Cause

The root cause is the absence of a re-entrancy guard in the local-delivery path. The stack treats loopback-style delivery as a synchronous function call rather than queuing the reply for a fresh work-queue iteration, violating the expectation that input processing returns before a reply is dispatched.

Attack Vector

Exploitation requires local access to the Zephyr shell and user interaction to issue the net ping command against the device's own IPv4 address. The vulnerability does not yield code execution or confidentiality impact but produces a high-availability impact through device crash. Network-based triggering is not described in the advisory.

The Zephyr Project Security Advisory GHSA-6fcc-8rwr-w7xx documents the recursion behavior and provides remediation guidance.

Detection Methods for CVE-2026-1681

Indicators of Compromise

• Unexpected device resets or kernel panics correlated with shell activity invoking net ping
• System work-queue stack-overflow faults reported in Zephyr console logs
• Crash dumps showing recursive frames within the IPv4 input handler and ICMP echo-reply path

Detection Strategies

• Audit firmware builds to identify images that enable the Zephyr shell with the net ping command compiled in
• Inspect device logs and serial console output for repeated stack-overflow assertions tied to network input processing
• Review device telemetry for unexplained reboots that follow administrator interaction with the network shell

Monitoring Recommendations

• Centralize Zephyr device console and crash logs to detect stack guard violations across the fleet
• Track firmware versions across deployed devices to confirm which units include the patched network stack
• Alert on repeated device resets that coincide with maintenance or diagnostic sessions

How to Mitigate CVE-2026-1681

Immediate Actions Required

• Restrict access to the Zephyr shell on production devices to trusted operators only
• Disable the net ping shell command in firmware builds where diagnostic ping is not required
• Avoid pinging a device's own IPv4 address until the patched Zephyr release is deployed

Patch Information

Refer to the upstream Zephyr Project Security Advisory GHSA-6fcc-8rwr-w7xx for the fixed commit references and affected version ranges. Rebuild and redeploy firmware against a Zephyr release that includes the re-entrancy fix in the IPv4 input path.

Workarounds

• Remove or CONFIG-disable the network shell subsystem in production firmware images
• Increase the system work-queue stack size as a partial mitigation, recognizing that this only raises the recursion threshold rather than eliminating the defect
• Document operational guidance instructing technicians not to ping the device's own assigned IPv4 address

# Configuration example: disable the net shell in prj.conf to remove the attack surface
CONFIG_NET_SHELL=n
CONFIG_SHELL=n