Key points
- CVE-2026-102692 affects RIOT OS versions prior to 2026.07.
- The flaw enables out-of-bounds memory access through oversized Block2 options.
- A verified fix exists in the master branch and version 2026.07.
RIOT OS versions older than 2026.07 contain a critical security flaw that allows remote attackers to corrupt memory or cause denial of service. The National Vulnerability Database rates CVE-2026-102692 as 9.1, indicating severe risk. The issue stems from how the nanocoap library handles CoAP Block2 option values. Developers have confirmed a fix is available in the 2026.07 release and later commits on the master branch.
In plain English
The bug occurs because the system fails to enforce a size limit on specific network packets. When a remote client sends a malformed request with an oversized block number, the software calculates an invalid memory range. This calculation error happens because the block offset multiplication overflows on 32-bit targets. The oversized value moves from one function to another without proper validation. This allows an attacker to access memory locations outside the intended bounds, leading to crashes or data corruption.
The background
RIOT is an open-source operating system designed for microcontrollers and Internet of Things devices. It is widely used in embedded systems where resource constraints are common. The vulnerability was identified in the nanocoap component, which handles constrained application protocol communications. The affected code baseline is commit aeeae69e on the master branch. The flaw leverages weaknesses classified as integer overflow and out-of-bounds write, according to CWE-190 and CWE-787 definitions.
What changes now
Users running RIOT OS versions before 2026.07 are exposed to this remote attack vector. The vendor has released version 2026.07, which includes the necessary code changes to fix the issue. The fix ensures that block number limits are strictly enforced. This prevents the overflow condition that previously allowed invalid slice ranges. Teams should verify their current version against this threshold to determine if they are vulnerable.
Who needs to act first
Security teams should prioritize updating embedded devices that expose CoAP services to untrusted networks. Systems facing the internet or public Wi-Fi require immediate attention. Before applying updates, create backups of device configurations to prevent operational disruption. Test the new firmware in a isolated environment to ensure compatibility with existing hardware. If immediate patching is impossible, restrict network access to trusted sources only. Monitor logs for unusual traffic patterns that might indicate exploitation attempts.
What to do and how to stay safe: RIOT OS
- Inventory all RIOT OS devices and check their current version against 2026.07.
- Update vulnerable devices to the latest patched version as soon as possible.
- Restrict network access to CoAP services to trusted internal networks only.
- Monitor system logs for signs of malformed packets or unexpected crashes.
Step-by-step guide: 7 Configuration Errors That Expose Systems to Zero-Day Exploits
General security guidance from the Vuln Post newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is the CVE ID for this RIOT OS vulnerability?
The vulnerability is tracked as CVE-2026-102692 in the National Vulnerability Database.
Which versions of RIOT OS are affected by this flaw?
All versions of RIOT OS prior to 2026.07 are affected by this security issue.
Is there a fix available for CVE-2026-102692?
Yes, the fix is included in RIOT OS version 2026.07 and later master commits.
