CVE-2026-49868 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, _parse_reply() in sys/net/application_layer/dhcpv6/client.c omits minimum-length validation before passing IA_PD and IA_NA option bodies to sub-option parsers. A malicious or compromised DHCPv6 server can send a REPLY with an option length smaller than the required structure while MODULE_DHCPV6_CLIENT_IA_PD is enabled, causing _parse_ia_pd_option to read past the option body, size_t underflow, and unbounded out-of-bounds heap reads that can crash the device and may expose or corrupt memory. This issue is fixed in version 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 IPv6 support via DHCPv6. Within this architecture, the dynamic host configuration protocol client implementation relies on parsing various option structures to configure network interfaces correctly. A critical security flaw exists in the _parse_reply() function located within sys/net/application_layer/dhcpv6/client.c, which handles incoming DHCPv6 messages from servers. This vulnerability arises specifically when the MODULE_DHCPV6_CLIENT_IA_PD feature is enabled, allowing the system to process Identity Association for Prefix Delegation options used for IPv6 prefix assignment in network environments such as 6LoWPAN or mesh networks.
The core technical deficiency lies in the absence of minimum-length validation before processing IA_PD and IA_NA option bodies. When a DHCPv6 server sends a REPLY message, the client parses these options to extract configuration data. However, the code fails to verify that the length field of the option body meets the structural requirements for sub-option parsing. Consequently, if a malicious or compromised DHCPv6 server transmits an option with a length value smaller than required by the internal structure definitions, the parser proceeds without checking bounds. This oversight leads directly to out-of-bounds memory access patterns where the parser attempts to read data beyond the allocated buffer boundaries of the option body.
This lack of validation results in severe operational consequences including size_t underflow conditions and unbounded heap reads. The underflow occurs because arithmetic operations involving the malformed length field can wrap around, leading to incorrect pointer calculations or loop iterations that exceed memory limits. These out-of-bounds accesses allow an attacker who controls a DHCPv6 server on the local network segment to read arbitrary contents from the device's heap memory. Such information disclosure can expose sensitive cryptographic keys, session tokens, or internal application data stored in adjacent memory regions. Furthermore, the corruption of memory state and stack integrity often leads to immediate denial of service by crashing the microcontroller process or causing undefined behavior that disrupts network connectivity and system stability.
From a classification perspective, this vulnerability aligns with CWE-125 Out-of-bounds Read due to insufficient validation of input data lengths and CWE-682 Incorrect Calculation which encompasses the size_t underflow issues resulting from improper arithmetic on untrusted length fields. In terms of attack vectors, it falls under MITRE ATT&CK technique T1498 Network Denial of Service as a primary impact, while also supporting information gathering techniques if memory contents are successfully exfiltrated through repeated exploitation attempts leveraging the DHCPv6 protocol channel. The vulnerability is particularly dangerous in constrained environments where RIOT operates because recovery from such crashes may require full device rebooting or manual intervention, impacting availability significantly.
Mitigation strategies primarily involve upgrading to version 2026.07 of the RIOT operating system which contains patches for this specific parsing logic. For systems unable to upgrade immediately, network segmentation is recommended to restrict DHCPv6 server access only to trusted infrastructure components that are not susceptible to compromise or malicious manipulation. Additionally, implementing strict input validation at the application layer before passing data to lower-level parsers can provide defense in depth, although upgrading remains the most effective remediation path given the low-level nature of the flaw within the network stack implementation.