CVE-2026-26459 in ccoap
Summary
by MITRE • 08/27/2026
ccoap 77f55c4b466e99327c24ace8a2913d3ba7e2ccd5 contains a vulnerability in the option parsing logic that causes a segmentation fault when processing malformed COAP messages with insufficient option data.
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Analysis
by VulDB Data Team • 08/27/2026
The Coap library, identified by commit hash 77f55c4b466e99327c24ace8a2913d3ba7e2ccd5, contains a critical flaw within its protocol option parsing logic. This vulnerability manifests as a segmentation fault when the application processes malformed Constrained Application Protocol messages that contain insufficient or improperly formatted option data. The CoAP standard relies on a compact binary format where options are encoded in a variable-length manner to optimize bandwidth usage for constrained networks. However, this implementation fails to adequately validate the length and bounds of these optional fields before attempting to access them in memory. When a malicious actor sends a crafted packet with truncated or malformed option headers, the parser attempts to read beyond the allocated buffer boundaries, leading to an invalid memory access that crashes the process.
This type of vulnerability is classified under CWE-125, which describes Out-of-bounds Read vulnerabilities. The root cause lies in the absence of rigorous boundary checks during the parsing phase of the CoAP message structure. In a typical secure implementation, the parser would verify that the remaining buffer length is sufficient to contain the declared option value before dereferencing pointers or copying data. Without these safeguards, the application assumes valid input from network sources, violating the principle of defensive programming. This flaw allows an attacker who can inject packets into the communication path between CoAP clients and servers to trigger a denial of service condition by causing the target process to terminate unexpectedly.
From an operational perspective, this vulnerability poses a significant risk to systems relying on lightweight IoT communications via UDP or TCP-based transports for CoAP. Since segmentation faults result in immediate application termination, repeated exploitation can lead to persistent unavailability of services such as device management, sensor data aggregation, or smart home automation hubs that utilize the affected library. Attackers do not require authentication to exploit this flaw if the service is exposed on a network interface accessible from external sources. The impact extends beyond simple availability loss; in some contexts, repeated crashes may interfere with logging mechanisms or trigger automatic restarts that mask evidence of the attack, complicating forensic analysis and incident response efforts.
The exploitation technique aligns with ATT&CK tactic T1498, Network Denial of Service, specifically sub-technique T1498.003 which involves flooding a target to cause degradation or destruction of service through protocol abuse. By sending specially crafted malformed packets that trigger the segmentation fault, an adversary can effectively take down critical infrastructure components without needing elevated privileges or complex exploit chains. This is particularly dangerous in IoT environments where devices often have limited resources for monitoring and may lack automated patching capabilities, making them susceptible to prolonged outages if this vulnerability remains unaddressed.
Mitigation strategies should prioritize immediate updates to the Coap library version that includes fixes for option parsing validation. Developers must ensure that all incoming network data is validated against expected schema constraints before processing. Implementing strict length checks on every variable-length field in the protocol parser will prevent out-of-bounds reads. Additionally, deploying input validation at the network perimeter using intrusion detection systems can help identify and block malformed packets characteristic of this exploit pattern. For long-term resilience, adopting fuzz testing methodologies during development cycles can uncover similar edge cases where malformed inputs lead to crashes or undefined behavior, ensuring that future versions maintain robustness against protocol-level abuse.