Memory Exhaustion in Eclipse Wakaama CoAP Block1 Handler

Executive Summary

CVE-2026-58465 is an unbounded memory allocation vulnerability in the Eclipse Wakaama library's CoAP Block1 handler. It occurs because the server does not enforce any maximum total size limit when processing a sequence of Block1 PUT requests with incrementing block numbers. An unauthenticated remote attacker can exploit this by sending many such requests to the registration endpoint over UDP, causing the server to repeatedly reallocate and grow a memory buffer without limits.

This results in the server exhausting its memory resources, leading to a denial of service condition.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Impact Analysis

This vulnerability can impact you by allowing unauthenticated attackers to cause a denial of service on your server running Eclipse Wakaama. By exploiting the unbounded memory allocation flaw, attackers can exhaust the server's memory, potentially causing it to crash or become unresponsive.

This can disrupt services relying on the affected server, leading to downtime and loss of availability.

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Detection Guidance

This vulnerability can be detected by monitoring for unusual or excessive Block1 PUT requests with incrementing block numbers targeting the registration endpoint over UDP. Such traffic patterns may indicate an attempt to exploit the unbounded memory allocation flaw.

Network detection can involve capturing and analyzing CoAP traffic on UDP ports used by the Eclipse Wakaama server, looking specifically for sequences of Block1 PUT requests with increasing block numbers.

Suggested commands include using packet capture tools like tcpdump or Wireshark to filter and inspect CoAP Block1 PUT requests:

• tcpdump -i <interface> udp port <CoAP_port> -w capture.pcap
• tshark -r capture.pcap -Y "coap && coap.opt.block1" -T fields -e coap.opt.block1.num

These commands help capture and analyze CoAP Block1 options to identify sequences of incrementing block numbers that may indicate exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include applying the official patch or update that introduces a configurable maximum message size limit (LWM2M_COAP_MAX_MESSAGE_SIZE) to prevent unbounded memory allocation.

This patch causes the server to respond with a COAP_413_ENTITY_TOO_LARGE error when a Block1 message exceeds the allowed size, effectively preventing memory exhaustion.

If patching is not immediately possible, consider implementing network-level controls such as rate limiting or filtering UDP traffic to the registration endpoint to block suspicious sequences of Block1 PUT requests.

Monitoring and alerting on unusual CoAP traffic patterns can also help detect and respond to exploitation attempts promptly.

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