CVE-2025-12899: Zephyr Network Stack Info Disclosure Flaw

CVE-2025-12899 Overview

A type confusion vulnerability exists in the Zephyr RTOS network stack that allows an IPv4 packet containing ICMP type 128 to be misclassified as an ICMPv6 Echo Request. This flaw results in an out-of-bounds memory read and creates a potential information-leak vulnerability in the networking subsystem. The vulnerability is classified under CWE-843 (Access of Resource Using Incompatible Type), indicating improper handling of protocol type identification within the network stack.

Critical Impact

Remote attackers can exploit this vulnerability to leak sensitive memory contents from affected Zephyr RTOS devices by sending specially crafted IPv4 packets, potentially exposing cryptographic keys, configuration data, or other sensitive information stored in memory.

Affected Products

• Zephyr RTOS (network stack component)
• Devices and systems running Zephyr's networking subsystem
• IoT devices utilizing Zephyr's IPv4/IPv6 dual-stack implementation

Discovery Timeline

• 2026-01-30 - CVE-2025-12899 published to NVD
• 2026-02-04 - Last updated in NVD database

Technical Details for CVE-2025-12899

Vulnerability Analysis

This vulnerability stems from a type confusion issue in Zephyr's network stack where the protocol identification logic fails to properly distinguish between IPv4 ICMP packets and ICMPv6 Echo Requests. When an IPv4 packet is crafted with ICMP type 128 (which corresponds to ICMPv6 Echo Request in the ICMPv6 specification), the Zephyr network stack incorrectly processes it as an ICMPv6 packet.

The fundamental issue lies in how the network stack handles ICMP type field validation without first verifying the IP version. ICMP type 128 is undefined in the IPv4 ICMP specification but is a valid ICMPv6 Echo Request type. When the stack misclassifies this packet, it attempts to read ICMPv6-specific header fields from what is actually an IPv4 packet structure, leading to out-of-bounds memory access.

Root Cause

The root cause is a type confusion vulnerability (CWE-843) in the ICMP packet processing logic. The network stack's packet classifier does not adequately verify the IP protocol version before processing ICMP type fields. This allows an attacker to force the stack into interpreting IPv4 packet data using ICMPv6 parsing routines, which expect a different memory layout and header structure.

The misalignment between the expected ICMPv6 header structure and the actual IPv4 packet content causes the code to read memory beyond the intended packet boundaries, potentially leaking adjacent memory contents in error responses or internal processing.

Attack Vector

The attack can be executed remotely over the network without authentication. An attacker constructs a malformed IPv4 packet with:

1. A valid IPv4 header indicating ICMP as the protocol
2. An ICMP payload with type field set to 128 (ICMPv6 Echo Request type)
3. Carefully crafted packet content to maximize information disclosure

When the vulnerable Zephyr device receives this packet, the type confusion causes the network stack to process it incorrectly. The out-of-bounds read may expose sensitive memory contents through:

• Error response packets that include portions of leaked memory
• Side-channel timing differences based on memory contents
• Crash dumps or debugging information if the device has monitoring enabled

The attack does not require user interaction and can be performed by any network-adjacent attacker capable of sending crafted packets to the target device.

Detection Methods for CVE-2025-12899

Indicators of Compromise

• Unusual IPv4 ICMP packets with type 128 arriving at Zephyr-based devices
• Unexpected memory access patterns or crashes in the network stack
• Anomalous ICMP response packets that may contain leaked memory data
• Increased network error rates or malformed packet logs from affected devices

Detection Strategies

• Deploy network intrusion detection rules to identify IPv4 packets with ICMP type 128, which is invalid for IPv4
• Monitor for unusual ICMP traffic patterns targeting embedded or IoT devices running Zephyr RTOS
• Implement packet inspection at network boundaries to filter malformed ICMP packets before they reach vulnerable devices
• Enable verbose logging on Zephyr devices to capture packet processing anomalies

Monitoring Recommendations

• Configure network monitoring tools to alert on IPv4 ICMP packets with type values outside the valid IPv4 ICMP range (0-18, 30, 37-43)
• Establish baseline network behavior for IoT and embedded devices to detect anomalous traffic patterns
• Review firewall and IDS logs for blocked or flagged ICMP packets targeting Zephyr-based infrastructure
• Consider network segmentation to isolate vulnerable IoT devices from untrusted network segments

How to Mitigate CVE-2025-12899

Immediate Actions Required

• Review the GitHub Security Advisory for official patch information and affected versions
• Implement network-level filtering to block IPv4 ICMP packets with invalid type values, particularly type 128
• Isolate affected Zephyr-based devices behind firewalls that perform deep packet inspection
• Prioritize firmware updates for internet-facing or critical Zephyr RTOS deployments

Patch Information

The Zephyr Project has published security advisory GHSA-c2vg-hj83-c2vg addressing this vulnerability. Organizations should consult the official GitHub Security Advisory for specific patch versions and upgrade instructions. Firmware updates should be tested in a non-production environment before deployment to ensure compatibility with existing device configurations.

Workarounds

• Deploy firewall rules at network boundaries to filter IPv4 ICMP packets with type 128 before they reach vulnerable devices
• If ICMPv6 is not required, consider disabling IPv6 functionality on affected devices to reduce attack surface
• Implement network segmentation to isolate IoT and embedded devices from untrusted network segments
• Use intrusion prevention systems (IPS) to automatically block suspicious ICMP traffic patterns

# Example iptables rule to block malformed IPv4 ICMP type 128 packets
iptables -A INPUT -p icmp --icmp-type 128 -j DROP
iptables -A FORWARD -p icmp --icmp-type 128 -j DROP