RIOT: nanocoap_fileserver ignores response initialization failure, leading to reachable assertion

published 2026-10-09 30 d ago modified 2026-10-16 23 d ago also EUVD-2026-95933

cvss: 7.5; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits: 0; none known

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.

Patch / fix

links 2

github.com/RIOT-OS/RIOT@d3a4728 commit
github.com/RIOT-OS/RIOT#22745 pull request

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 26 d ago (2026-10-13)

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

RIOT-OS RIOT

Classification

Weakness

CWE-252 Unchecked Return Value
CWE-617 Reachable Assertion

References

Sources

CVE List CVE-2026-107838
NVD CVE-2026-107838

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary