Integer Underflow in OpenWrt Emergency Access Daemon

Compliance Impact

This vulnerability causes a denial of service by crashing the Emergency Access Daemon on affected OpenWrt devices. It does not directly impact confidentiality or integrity of data, as it does not allow unauthorized data access or modification.

However, disruption of emergency remote-access capabilities could indirectly affect compliance with standards that require availability and reliability of critical systems, such as HIPAA's requirements for system availability or GDPR's requirements for data processing continuity.

Since the vulnerability does not involve data breach or unauthorized data disclosure, its impact on compliance with data protection regulations like GDPR or HIPAA is limited to potential service availability concerns.

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Executive Summary

This vulnerability exists in OpenWrt, a Linux operating system for embedded devices. Before version 25.12.5, there is an integer underflow in the function handle_send_a() of the Emergency Access Daemon. An unauthenticated attacker on the local network can exploit this by sending a specially crafted UDP packet. The crafted packet causes the message length to underflow before a bounds check, resulting in a very large size being passed to the memcpy function, which crashes the daemon.

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Impact Analysis

The vulnerability allows any unauthenticated attacker on the local network to crash the Emergency Access Daemon by sending a single crafted UDP packet. This results in a denial of service (DoS) condition, making the affected service unavailable.

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade OpenWrt to version 25.12.5 or later, where the issue has been fixed.

Since the vulnerability allows unauthenticated local network attackers to crash the Emergency Access Daemon, restricting access to the local network or disabling the daemon until the update can be applied may reduce risk.

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Detection Guidance

This vulnerability can be detected by monitoring for unusual crashes or denial of service of the Emergency Access Daemon (ead) on OpenWrt devices, especially after receiving UDP packets on the local network.

Since the vulnerability is triggered by a crafted UDP packet with a message length field set to zero, you can detect attempts by capturing and inspecting UDP traffic targeting the ead service.

Suggested commands to detect potential exploitation attempts include:

• Using tcpdump to capture suspicious UDP packets on the local network: tcpdump -i <interface> udp and port <ead_port>
• Filtering for UDP packets with a zero length field in the payload would require custom packet inspection tools or scripts, as the crafted packet sets the length field to zero to trigger the underflow.
• Monitoring system logs for crashes or restarts of the ead daemon can also indicate exploitation attempts.

Note that no specific detection commands are provided in the resources, so detection relies on network traffic analysis and monitoring daemon stability.

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