CVE-2026-102692 in RIOT
Summary
by MITRE • 10/16/2026
RIOT is an open-source microcontroller operating system designed for Internet of Things devices and other embedded systems. Prior to 2026.07, nanocoap accepts oversized CoAP Block2 option values without enforcing the 20-bit maximum block number, allowing block offset multiplication to overflow on 32-bit targets. The affected master baseline is commit aeeae69e; the verified fix is later on master and remains unreleased. The oversized value passes from coap_get_blockopt() to coap_block_slicer_init(). A remote CoAP client can send a malformed Block2 option that produces an invalid slice range and can cause out-of-bounds memory access, denial of service, or memory corruption. This vulnerability is fixed in 2026.07.
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Analysis
by VulDB Data Team • 10/16/2026
The RIOT operating system serves as a foundational software layer for Internet of Things devices and embedded systems, providing essential networking capabilities including the Constrained Application Protocol implementation known as nanocoap. Within this ecosystem, the handling of CoAP Block2 options is critical for efficient data transfer in constrained environments where large payloads must be segmented into smaller chunks. The vulnerability identified prior to version 2026.07 resides specifically within the logic that processes these block numbers during incoming requests from remote clients. This component is responsible for determining how much data remains to be received and managing the memory buffers allocated for reassembling or processing these segments.
The core technical flaw stems from a failure in input validation regarding the Block2 option value. Specifically, nanocoap does not enforce the strict 20-bit maximum limit defined by the CoAP specification for block numbers. When a remote attacker sends a malformed request containing an oversized Block2 value, this invalid integer is passed directly from the coap_get_blockopt function to the coap_block_slicer_init routine without adequate boundary checks. On 32-bit target architectures, which are common in many embedded devices, this lack of validation allows the block offset multiplication operation to overflow. This arithmetic error results in a miscalculated slice range that does not correspond to valid memory addresses or buffer sizes within the application context.
The operational impact of this vulnerability is severe and multifaceted. The immediate consequence is an out-of-bounds memory access, which can lead to arbitrary code execution if the attacker can control the data written to the unintended memory location. In less exploitable scenarios, the overflow causes a denial of service by crashing the RIOT process or the entire device due to illegal memory operations. Furthermore, the corruption of internal state variables related to block slicing can destabilize subsequent network transactions, leading to persistent instability even after the initial malicious packet is processed. This represents a significant risk for any IoT deployment relying on CoAP for telemetry data collection or configuration updates over constrained networks like 6LoWPAN or LoRaWAN.
From a classification perspective, this vulnerability aligns with CWE-190 Integer Overflow or Wraparound and CWE-787 Out-of-bounds Write, as the root cause is an unchecked arithmetic operation leading to memory safety violations. In terms of attack vectors, it falls under ATT&CK technique T1190 Exploit Public-Facing Application, given that CoAP services are often exposed on network interfaces accessible from external or untrusted networks. The vulnerability allows for remote exploitation without authentication in many default configurations where CoAP endpoints are open to general traffic.
Mitigation strategies must prioritize immediate patching once the 2026.07 release becomes available, as this version contains the verified fix that enforces proper bounds checking on Block2 option values. For environments unable to upgrade immediately, network-level defenses such as ingress filtering or application firewalls should be configured to inspect CoAP packets and drop those with block numbers exceeding valid limits. Developers integrating nanocoap into custom builds must also ensure they are using a version of the library that includes these validation checks before deployment in production IoT devices. Regular security audits of embedded networking stacks are recommended to identify similar input handling flaws in other protocol implementations within the RIOT codebase.