CVE-2026-107836 (GCVE-0-2026-107836)

Vulnerability from cvelistv5 – Published: 2026-10-09 17:49 – Updated: 2026-10-09 18:00
VLAI
Title
RIOT: nanoCoAP Block2 client slice handling underflows on inconsistent server-controlled block size
Summary
RIOT is an open-source microcontroller operating system designed for Internet of Things devices and other embedded systems. In 2026.07 and earlier, the nanoCoAP client function nanocoap_sock_get_slice() in sys/net/application_layer/nanocoap/sock.c accepts a Block2 response when _block_cb() sees the expected block number without also verifying that the server-controlled szx and derived offset match the requested block geometry. A malicious CoAP server can return the expected block number with a larger block size, causing the derived offset to exceed the client slice offset and making ctx->offset - offset underflow in _2buf_slice(). The resulting buffer-relative calculation can read before the payload buffer and crash the client, causing denial of service and potentially exposing adjacent memory. No fixed release is available as of this review.
Severity
7.1 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-09 17:59 UTC
CWE
  • CWE-125 - Out-of-bounds Read
  • CWE-191 - Integer Underflow (Wrap or Wraparound)
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7642 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
RIOT-OS RIOT Affected: <= 2026.07
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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