CVE-2026-0849: Zephyr Crypto Driver Buffer Overflow Bug

CVE-2026-0849 Overview

CVE-2026-0849 is a stack buffer overflow vulnerability in the Zephyr RTOS crypto driver for ATAES132A devices. Malformed ATAES132A responses with an oversized length field overflow a 52-byte stack buffer in the Zephyr crypto driver, allowing a compromised device or bus attacker to corrupt kernel memory and potentially hijack execution.

Critical Impact

A physical attacker with access to the I2C/SPI bus or a compromised ATAES132A device can trigger a stack buffer overflow, corrupting kernel memory and potentially achieving arbitrary code execution on affected Zephyr-based embedded systems.

Affected Products

• Zephyr RTOS (versions with ATAES132A crypto driver support)
• Embedded systems utilizing the Zephyr ATAES132A driver
• IoT devices with ATAES132A hardware security modules

Discovery Timeline

• 2026-03-16 - CVE CVE-2026-0849 published to NVD
• 2026-03-17 - Last updated in NVD database

Technical Details for CVE-2026-0849

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), a classic buffer overflow condition. The Zephyr RTOS crypto driver for ATAES132A secure memory devices fails to properly validate the length field in responses received from the hardware. When processing responses from the ATAES132A device, the driver copies data into a fixed 52-byte stack buffer without adequately verifying that the declared response length does not exceed this buffer size.

The physical attack vector requires an adversary to either have physical access to the communication bus (I2C or SPI) connecting the microcontroller to the ATAES132A chip, or to have compromised the ATAES132A device itself. This limits exploitation scenarios to hardware-level attacks but remains a significant concern for embedded security applications where the ATAES132A is specifically deployed as a hardware security element.

Root Cause

The root cause is insufficient input validation in the ATAES132A driver's response handling code. The driver allocates a 52-byte buffer on the stack to receive response data from the cryptographic device but trusts the length field provided in the response without bounds checking. When a malformed response specifies a length greater than 52 bytes, the subsequent memory copy operation writes beyond the allocated buffer, corrupting adjacent stack memory including saved registers and return addresses.

Attack Vector

Exploitation requires physical access to the target system's hardware bus infrastructure. An attacker can inject malicious responses on the I2C or SPI bus by either:

1. Bus Tampering: Physically intercepting and manipulating communications between the microcontroller and the ATAES132A device
2. Device Compromise: Replacing or reprogramming the ATAES132A device to emit malformed responses
3. Man-in-the-Middle: Inserting a malicious device between the legitimate ATAES132A and the microcontroller

The vulnerability manifests when the driver processes a response containing an oversized length field. By carefully crafting the overflow payload, an attacker can overwrite the return address on the stack, potentially redirecting execution to attacker-controlled code. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-0849

Indicators of Compromise

• Unexpected system crashes or reboots on Zephyr-based devices during cryptographic operations
• Anomalous I2C/SPI bus traffic with unusually large response packets from ATAES132A addresses
• Memory corruption indicators in system logs or fault handlers
• Unexpected code execution behavior following ATAES132A transactions

Detection Strategies

• Implement hardware bus monitoring to detect oversized response packets exceeding 52 bytes from ATAES132A devices
• Enable Zephyr's stack canary protection (CONFIG_STACK_CANARIES=y) to detect stack buffer overflows at runtime
• Monitor for repeated fault handler invocations that may indicate exploitation attempts
• Review firmware integrity to ensure crypto driver binaries match known-good versions

Monitoring Recommendations

• Deploy bus analyzers or logic analyzers on I2C/SPI buses in high-security deployments to detect anomalous traffic patterns
• Enable comprehensive logging of cryptographic operation failures and system faults
• Implement periodic integrity checks on firmware images to detect unauthorized modifications
• Monitor physical access to deployed devices through tamper-evident enclosures or intrusion detection

How to Mitigate CVE-2026-0849

Immediate Actions Required

• Audit deployments using the Zephyr ATAES132A crypto driver to identify vulnerable systems
• Apply physical security controls to restrict access to I2C/SPI buses on affected devices
• Enable stack protection mechanisms (CONFIG_STACK_CANARIES) as a defense-in-depth measure
• Review the official security advisory for patches and apply firmware updates as available

Patch Information

Consult the GitHub Security Advisory for official patch information and updated Zephyr versions that address this vulnerability. Organizations should update to patched Zephyr versions that include proper bounds checking on ATAES132A response length fields.

Workarounds

• Implement physical security measures to prevent unauthorized access to device hardware and communication buses
• Consider disabling the ATAES132A driver if not required for your application until patches can be applied
• Enable additional runtime protections such as memory protection units (MPU) where supported by the hardware platform
• Implement application-level validation of cryptographic responses before passing to the driver layer

# Enable stack canary protection in Zephyr prj.conf
CONFIG_STACK_CANARIES=y
CONFIG_HW_STACK_PROTECTION=y
CONFIG_MPU_STACK_GUARD=y