CVE-2026-5856

HIGHPre-NVD 7.17.1—
EchelonGraph scoreHIGH confidence

Score 7.1 from GitHub Security Advisory (severity: HIGH) published 2026-08-07. the CNA's CVSS baseline 7.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cna:vulncheck, epss, ghsa
Trending — 3 sources updated this week
7.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.1Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Contiki-NG's DNS/mDNS resolver skip_name() in os/services/resolv/resolv.c walks DNS wire-format name labels with no packet-boundary check, and the caller in newdata() invokes it in a loop iterating nquestions times from the attacker-controlled DNS header before validating the transaction ID. An attacker who sets nquestions higher than the number of complete questions present causes skip_name() to walk past the UDP packet buffer, and the returned pointer is cast to struct dns_answer * for further memory reads. On builds with RESOLV_CONF_SUPPORTS_MDNS enabled, any peer on the local segment can trigger the read unauthenticated via a multicast UDP 5353 packet with no outstanding query required; on standard DNS builds an attacker who can inject a UDP response from port 53 during an outstanding query can trigger the same read. Impact is out-of-bounds read of uip_buf and adjacent memory, disclosing memory contents or crashing the resolver.

CVSS v3
7.1
EG Score
7.1(high)
EG Risk
32(Track)
EG Risk 32/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity71% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
17%
KEV
Not listed

Published

August 6, 2026

Last Modified

August 14, 2026

Advisory Details (3)

Auto-updated Aug 6, 2026
Upstream fix merged — awaiting tagged release. Sources: github_commit, github_pr.
github_pr

resolv: add bounds checking to DNS name parsing

Fix merged in contiki-ng/contiki-ng PR #3169 on 2026-07-08 — awaiting tagged release

https://github.com/contiki-ng/contiki-ng/pull/3169
github_commit

commit 04a3f0a0067d (contiki-ng/contiki-ng)

Fix landed in contiki-ng/contiki-ng commit 04a3f0a0067d — awaiting tagged release

https://github.com/contiki-ng/contiki-ng/commit/04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe
generic

GitHub - contiki-ng/contiki-ng: Contiki-NG: The OS for Next Generation IoT Devices · GitHub

https://github.com/contiki-ng/contiki-ng

Vendor Advisories for CVE-2026-5856(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 29× in last 7d / 62× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-08-21 01:59 UTCEG score recompute
  2. 2026-08-21 01:59 UTCGHSA enrichment
  3. 2026-08-20 22:55 UTCEPSS rescore
  4. 2026-08-20 14:21 UTCGHSA enrichment
  5. 2026-08-20 02:43 UTCEG score recompute
  6. 2026-08-20 02:43 UTCGHSA enrichment
  7. 2026-08-19 17:04 UTCEPSS rescore
  8. 2026-08-19 14:59 UTCGHSA enrichment
  9. 2026-08-19 03:20 UTCGHSA enrichment
  10. 2026-08-18 15:41 UTCEG score recompute
  11. 2026-08-18 15:41 UTCGHSA enrichment
  12. 2026-08-18 13:48 UTCEPSS rescore
  13. 2026-08-18 02:32 UTCGHSA enrichment
  14. 2026-08-17 14:54 UTCEG score recompute
  15. 2026-08-17 14:54 UTCGHSA enrichment
  16. 2026-08-17 13:47 UTCEPSS rescore
  17. 2026-08-17 03:17 UTCGHSA enrichment
  18. 2026-08-16 15:39 UTCEG score recompute
  19. 2026-08-16 15:39 UTCGHSA enrichment
  20. 2026-08-16 14:56 UTCEPSS rescore
  21. 2026-08-16 04:02 UTCEG score recompute
  22. 2026-08-16 04:02 UTCGHSA enrichment
  23. 2026-08-15 16:25 UTCGHSA enrichment
  24. 2026-08-15 04:48 UTCEG score recompute
  25. 2026-08-15 04:48 UTCGHSA enrichment
Show 37 more
  1. 2026-08-15 01:30 UTCEPSS rescore
  2. 2026-08-14 17:10 UTCEG score recompute
  3. 2026-08-14 17:10 UTCGHSA enrichment
  4. 2026-08-14 13:13 UTCGHSA enrichment
  5. 2026-08-14 01:36 UTCEG score recompute
  6. 2026-08-14 01:36 UTCGHSA enrichment
  7. 2026-08-13 22:00 UTCEPSS rescore
  8. 2026-08-13 13:58 UTCGHSA enrichment
  9. 2026-08-13 02:18 UTCGHSA enrichment
  10. 2026-08-12 14:41 UTCEG score recompute
  11. 2026-08-12 14:41 UTCGHSA enrichment
  12. 2026-08-12 13:51 UTCEPSS rescore
  13. 2026-08-12 03:03 UTCGHSA enrichment
  14. 2026-08-11 15:25 UTCEG score recompute
  15. 2026-08-11 15:25 UTCGHSA enrichment
  16. 2026-08-11 03:48 UTCEG score recompute
  17. 2026-08-11 03:48 UTCGHSA enrichment
  18. 2026-08-11 00:00 UTCEPSS rescore
  19. 2026-08-10 16:11 UTCGHSA enrichment
  20. 2026-08-10 04:33 UTCGHSA enrichment
  21. 2026-08-09 16:56 UTCEG score recompute
  22. 2026-08-09 16:56 UTCGHSA enrichment
  23. 2026-08-09 13:46 UTCEPSS rescore
  24. 2026-08-09 05:19 UTCGHSA enrichment
  25. 2026-08-08 17:42 UTCEG score recompute
  26. 2026-08-08 17:42 UTCGHSA enrichment
  27. 2026-08-08 16:37 UTCEPSS rescore
  28. 2026-08-08 06:04 UTCGHSA enrichment
  29. 2026-08-07 18:27 UTCEG score recompute
  30. 2026-08-07 18:27 UTCGHSA enrichment
  31. 2026-08-07 17:47 UTCEG score recompute
  32. 2026-08-07 17:47 UTCGHSA enrichment
  33. 2026-08-07 09:59 UTCEG score recompute
  34. 2026-08-07 09:59 UTCGHSA enrichment
  35. 2026-08-06 22:22 UTCEG score recompute
  36. 2026-08-06 22:16 UTCEG score recompute
  37. 2026-08-06 22:15 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-5856?
CVE-2026-5856 is a high vulnerability published on August 6, 2026. Contiki-NG's DNS/mDNS resolver skipname() in os/services/resolv/resolv.c walks DNS wire-format name labels with no packet-boundary check, and the caller in newdata() invokes it in a loop iterating nquestions times from the attacker-controlled DNS header before validating the transaction ID. An…
When was CVE-2026-5856 disclosed?
CVE-2026-5856 was first published in the National Vulnerability Database on August 6, 2026, with the most recent update on August 14, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-5856 actively exploited?
CVE-2026-5856 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 82.9% of all scored CVEs.
What is the CVSS score of CVE-2026-5856?
CVE-2026-5856 has a CVSS v4.0 base score of 7.1 (CNA self-assessment; NVD's own analysis pending).
How do I remediate CVE-2026-5856?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-5856, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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