CVE-2020-13987

What it actually does

Out-of-bounds read in upper_layer_chksum during IP packet checksum calculation allows memory access beyond allocated buffers, resulting in denial of service via crash or undefined behavior.

Why it matters to the business

Network-connected embedded devices may experience unexpected restarts or outages, interrupting operations in IoT, industrial, and metering environments where uptime is critical.

How an attack unfolds

An attacker crafts a malformed IPv4 packet and sends it to a vulnerable device; the uIP stack invokes upper_layer_chksum which performs an out-of-bounds read while computing the checksum, causing the device to fault or hang.

How to fix it

Upgrade Contiki to a version containing the corrected uIP checksum logic; apply vendor patches for Siemens SENTRON devices; restrict direct IP exposure of affected systems until updated.

How to confirm the fix worked

Review source or binary for bounds checks in upper_layer_chksum; perform network fuzzing against checksum paths; confirm device remains stable under malformed packet tests after update.

Typical attack path

1. Identify reachable devices running affected uIP stack implementations
2. Craft and transmit a specially formed IP packet that triggers the checksum path
3. Observe device crash or unresponsiveness confirming successful denial of service

How to detect it

Inspect device logs or crash dumps for faults occurring during IP checksum processing; correlate spikes in malformed inbound packets with device reboots or loss of connectivity.

What your security team should do

• Prioritize patching or replacing affected Contiki-based and Siemens SENTRON devices given public disclosure and high availability impact
• Segment networks to limit unauthenticated IP traffic to embedded systems
• Monitor for device instability correlated with inbound IP traffic