CVE-2025-9557 Overview
CVE-2025-9557 is an out-of-bounds write vulnerability affecting the Zephyr real-time operating system (RTOS). The flaw enables attackers on an adjacent network to write beyond allocated buffer boundaries, which can lead to arbitrary code execution on impacted devices. On platforms that implement memory protection, the same condition produces a crash and a denial-of-service state instead of code execution. The vulnerability is tracked under CWE-120: Buffer Copy without Checking Size of Input. Zephyr maintainers published details in the GitHub Security Advisory GHSA-r3j3-c5v7-2ppf.
Critical Impact
An adjacent-network attacker can trigger an out-of-bounds write that results in arbitrary code execution or a denial-of-service crash on Zephyr-based embedded and IoT devices.
Affected Products
- Zephyr Project RTOS (see vendor advisory for affected version ranges)
- Embedded and IoT devices running vulnerable Zephyr builds
- Connected products that incorporate Zephyr networking stacks
Discovery Timeline
- 2025-11-26 - CVE-2025-9557 published to the National Vulnerability Database
- 2026-04-15 - Last updated in NVD database
Technical Details for CVE-2025-9557
Vulnerability Analysis
The vulnerability is a classic buffer copy without checking the size of the input, classified as [CWE-120]. Zephyr writes attacker-influenced data past the end of a fixed-size buffer in memory. The write corrupts adjacent memory structures used by the RTOS or application code. On devices without memory protection, attackers can craft input that overwrites return addresses, function pointers, or control structures to redirect execution. On devices that enforce memory protection through a memory protection unit (MPU) or memory management unit (MMU), the write traps and forces the system into a fault handler, halting normal operation.
Root Cause
The root cause is missing or insufficient bounds validation on data received over the network before it is copied into a destination buffer. The code path trusts a length field or assumes a maximum size that the input can exceed. Refer to the Zephyr security advisory GHSA-r3j3-c5v7-2ppf for the affected source files and commit references.
Attack Vector
The attack vector is adjacent network, meaning the attacker must share a logical network segment such as the same Wi-Fi network, Bluetooth piconet, or layer-2 broadcast domain as the target. No authentication or user interaction is required. The attacker sends a crafted network frame or packet whose size or content fields drive the vulnerable code path into writing beyond the destination buffer. Successful exploitation yields arbitrary code execution at the privilege level of the affected Zephyr task or, where memory protection is enabled, a device crash.
Detection Methods for CVE-2025-9557
Indicators of Compromise
- Unexpected reboots, hard faults, or watchdog resets on Zephyr-based devices following network activity
- Crash logs or core dumps referencing memory access violations in network processing code paths
- Anomalous outbound connections or process behavior from embedded devices after exposure to untrusted adjacent networks
Detection Strategies
- Inventory firmware builds and identify devices running vulnerable Zephyr versions against the advisory metadata
- Inspect adjacent-network traffic for malformed frames targeting Zephyr network services, including oversized length fields
- Correlate device crash telemetry with packet captures to identify exploitation attempts that result in denial of service
Monitoring Recommendations
- Forward Zephyr device logs and crash reports into a centralized analytics platform for correlation
- Monitor wireless and wired segments hosting embedded devices for unauthorized stations and suspicious broadcast traffic
- Track firmware version compliance continuously to ensure patched builds are deployed across the fleet
How to Mitigate CVE-2025-9557
Immediate Actions Required
- Identify all devices and products built on the Zephyr RTOS and confirm firmware versions in use
- Apply the patched Zephyr release referenced in GHSA-r3j3-c5v7-2ppf as soon as vendor builds are available
- Restrict device exposure to trusted network segments until patched firmware is deployed
Patch Information
The Zephyr Project published fix details in the GitHub Security Advisory GHSA-r3j3-c5v7-2ppf. Device manufacturers that integrate Zephyr must rebase onto the corrected upstream release and ship updated firmware to deployed devices.
Workarounds
- Isolate Zephyr devices on segmented networks or VLANs that block untrusted adjacent hosts
- Disable unused network services and protocols on Zephyr devices to reduce the reachable attack surface
- Enable hardware memory protection features such as MPU enforcement to convert exploitation into a recoverable fault rather than code execution
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
