CVE-2026-58465: Eclipse Wakaama CoAP Block1 Memory Exhaustion Denial of Service

Technical summary

The vulnerability exists in coap/block.c, specifically in the Block1 handler that manages incoming CoAP PUT requests fragmented into blocks. When processing a sequence of Block1 PUT requests targeting the registration endpoint, the implementation appends each block's payload to a reassembly buffer without enforcing a maximum cumulative size. An attacker can send blocks with incrementing block numbers over UDP, causing the buffer to grow without bound until server memory is exhausted. The flaw is reachable without authentication and does not require user interaction.

Business impact

A successful attack renders a Wakaama-based IoT management server unavailable, disrupting device provisioning, firmware updates, and remote management operations. In industrial IoT, smart city, or healthcare deployments where Wakaama manages large device fleets, this can cascade into operational downtime. Recovery requires manual service restart. The attack is trivial to execute—a single attacker with network access can degrade or eliminate service availability for legitimate device management tasks.

Affected systems

Eclipse Wakaama snapshots released before 2026-05-26 are vulnerable. Wakaama is used in embedded systems, IoT gateways, and device management platforms. Any deployment exposing a Wakaama server to untrusted networks—including internet-facing management endpoints—is at risk. The vulnerability is in a core protocol handler, so all Wakaama installations using CoAP Block1 transfers are potentially affected unless patched.

Exploitability

Exploitability is high. The attack requires only network access (no authentication, no credentials, no user interaction) and can be launched with standard CoAP tooling or a simple script. The attacker needs to know or guess the server's CoAP endpoint address and port. No special timing, race conditions, or system-specific tuning is required. A proof-of-concept is straightforward: rapidly send Block1 PUT requests with monotonically increasing block numbers until the server becomes unresponsive.

Remediation

Upgrade to Eclipse Wakaama snapshot/2026-05-26 or later. The fix enforces a maximum cumulative size limit on Block1 reassembly buffers, rejecting oversized transfers before memory exhaustion occurs. Verify the patch version against the official Eclipse Wakaama release notes and security advisories. Organizations unable to patch immediately should implement network-level controls: restrict CoAP access to trusted management networks, use firewalls to limit ingress on CoAP ports (typically UDP 5683), and monitor for unusual patterns of Block1 requests.

Patch guidance

Apply the update from Eclipse Wakaama snapshot/2026-05-26 or a later stable release. Test patched builds in a non-production environment to ensure compatibility with your device fleet and management workflows. Pay particular attention to any custom CoAP handlers or block-processing extensions you may have added; verify they work correctly with the updated core. Review release notes for any configuration changes related to block transfer limits. After patching, restart all affected Wakaama services and confirm normal device management operations resume.

Detection guidance

Monitor CoAP traffic for anomalous Block1 PUT sequences: repeated requests with incrementing block numbers from a single source, especially to the registration endpoint, may indicate an attack attempt. Track server memory and CPU usage during CoAP operations; a sustained spike without corresponding legitimate activity is suspicious. Implement CoAP-aware logging in your management stack to record block transfers; correlate high-volume or oversized block sequences with service degradation. Consider deploying CoAP firewalls or proxies that rate-limit or validate block sizes before they reach the server. For detection systems lacking CoAP inspection, watch for UDP traffic surges on port 5683 from external sources.

Why prioritize this

This is a HIGH-severity vulnerability affecting core IoT infrastructure. The combination of unauthenticated network access, no user interaction required, and direct impact on service availability (denial of service) makes it an urgent remediation target. IoT deployments often operate 24/7 and manage critical systems; downtime compounds over time and may trigger SLA violations or cascading failures. The ease of exploitation and low attacker skill barrier mean active exploitation is probable in internet-facing deployments. Prioritize patching for any externally accessible or DMZ-deployed Wakaama instances.

Risk score, explained

CVSS 3.1 score of 7.5 (HIGH) reflects: Attack Vector Network (remote exploitation possible), Attack Complexity Low (no special conditions), Privileges Required None (unauthenticated), User Interaction None (direct server impact), and Availability Impact High (denial of service). Confidentiality and Integrity are unaffected (the attack only exhausts memory, not exposing or corrupting data). The score accurately reflects the practical threat: a trivial-to-execute network denial-of-service attack on a widely-deployed IoT framework.

Frequently asked questions