CVE-2026-107838
HIGHDescription
RIOT is an open-source microcontroller operating system designed for Internet of Things devices and other embedded systems. From version 2023.07 through version 2026.07, nanocoap_fileserver callers in sys/net/application_layer/nanocoap/fileserver.c ignore a failure returned by _resp_init() when coap_build_reply() cannot fit a response header into the response buffer. A remote client can send a CoAP request with a sufficiently large extended token when nanocoap_token_ext is enabled, causing response initialization to fail while _get_file() or _get_directory() continues with stale response state. The path then reaches _calc_szx2() and its pdu->payload_len > reserve assertion, terminating the affected service or device task. No fixed release is available as of this review.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Low risk: more likely to be exploited than 26% of all known CVEs.
References
Related Vulnerabilities
Other CWE-252 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2005-4360 | High | 7.8 | 87% | - | - |
| CVE-2007-3798 | Critical | 9.8 | 70% | - | Fix |
| CVE-2010-0211 | Critical | 9.8 | 28% | - | Fix |
| CVE-2022-23626 | High | 8.5 | 9.9% | - | Fix |
| CVE-2019-10902 | High | 7.5 | 4.7% | - | - |
| CVE-2018-20216 | High | 7.5 | 3.9% | - | Fix |
Common questions
How do I fix CVE-2026-107838?
No published fix for CVE-2026-107838 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-107838 being actively exploited?
Not that we know of. CVE-2026-107838 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.34% is the estimated probability that it will be exploited in the next 30 days. That is higher than 26% of all scored CVEs.
How severe is CVE-2026-107838?
CVE-2026-107838 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-10-16.