CVE-2026-5856

HIGHPre-NVD 7.17.1—
EchelonGraph scoreMEDIUM confidence

Score 7.1 from GitHub Security Advisory (severity: HIGH) published 2026-08-07. A secondary CVSS source baseline 7.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
7.1EG
EchelonGraph verdictPlan mitigationSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 7.1Exploit: None knownExposed services: Not assessed

An upstream fix is merged but not yet released — mitigate (WAF / firewall / segmentation) until the release ships, then apply it.

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
7.1HIGHmedium confidence
EG Risk
32
EG Risk 32/100CISA SSVC

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%
CISA SSVC: Track at every mission impact level.
Action: An upstream fix is merged but not yet in a tagged release. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines until it ships, then apply the release.
EPSS PROB
0.3%
EPSS %ILE
19th
KEV
Not listed

CISA SSVCTrack at every mission impact level.

An upstream fix is merged but not yet in a tagged release. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines until it ships, then apply the release.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

August 6, 2026

Last Modified

September 16, 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 17× in last 7d / 88× 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.

Showing the most recent 100 of 205 total refreshes for this CVE.

  1. 2026-10-04 23:22 UTCEPSS rescore
  2. 2026-10-04 23:22 UTCGHSA enrichment
  3. 2026-10-04 05:48 UTCEG score recompute
  4. 2026-10-04 05:48 UTCGHSA enrichment
  5. 2026-10-03 14:26 UTCEPSS rescore
  6. 2026-10-03 01:03 UTCEG score recompute
  7. 2026-10-03 01:03 UTCGHSA enrichment
  8. 2026-10-02 17:56 UTCEPSS rescore
  9. 2026-10-02 09:38 UTCEG score recompute
  10. 2026-10-02 09:38 UTCGHSA enrichment
  11. 2026-10-01 19:50 UTCEPSS rescore
  12. 2026-10-01 10:55 UTCGHSA enrichment
  13. 2026-09-30 23:01 UTCEG score recompute
  14. 2026-09-30 23:01 UTCGHSA enrichment
  15. 2026-09-30 15:03 UTCEPSS rescore
  16. 2026-09-29 05:53 UTCEG score recompute
  17. 2026-09-29 05:53 UTCGHSA enrichment
  18. 2026-09-28 13:51 UTCEPSS rescore
  19. 2026-09-28 05:05 UTCGHSA enrichment
  20. 2026-09-27 17:28 UTCEG score recompute
  21. 2026-09-27 17:28 UTCGHSA enrichment
  22. 2026-09-26 15:59 UTCEPSS rescore
  23. 2026-09-25 04:21 UTCEG score recompute
  24. 2026-09-25 04:21 UTCGHSA enrichment
  25. 2026-09-24 11:24 UTCGHSA enrichment
Show 75 more
  1. 2026-09-23 23:47 UTCEG score recompute
  2. 2026-09-23 23:47 UTCGHSA enrichment
  3. 2026-09-23 17:54 UTCEPSS rescore
  4. 2026-09-23 12:09 UTCGHSA enrichment
  5. 2026-09-23 00:31 UTCEG score recompute
  6. 2026-09-23 00:31 UTCGHSA enrichment
  7. 2026-09-22 12:52 UTCGHSA enrichment
  8. 2026-09-22 01:02 UTCEG score recompute
  9. 2026-09-22 01:01 UTCGHSA enrichment
  10. 2026-09-21 12:46 UTCGHSA enrichment
  11. 2026-09-20 20:35 UTCEG score recompute
  12. 2026-09-20 20:35 UTCGHSA enrichment
  13. 2026-09-20 20:16 UTCEPSS rescore
  14. 2026-09-20 00:37 UTCEG score recompute
  15. 2026-09-20 00:37 UTCGHSA enrichment
  16. 2026-09-19 12:59 UTCGHSA enrichment
  17. 2026-09-19 01:11 UTCEG score recompute
  18. 2026-09-19 01:10 UTCGHSA enrichment
  19. 2026-09-18 19:28 UTCEPSS rescore
  20. 2026-09-18 13:12 UTCGHSA enrichment
  21. 2026-09-18 00:57 UTCEG score recompute
  22. 2026-09-18 00:57 UTCGHSA enrichment
  23. 2026-09-17 19:31 UTCEPSS rescore
  24. 2026-09-17 08:48 UTCGHSA enrichment
  25. 2026-09-16 21:10 UTCEG score recompute
  26. 2026-09-16 21:10 UTCGHSA enrichment
  27. 2026-09-16 14:08 UTCEPSS rescore
  28. 2026-09-16 05:15 UTCEPSS rescore
  29. 2026-09-16 03:44 UTCGHSA enrichment
  30. 2026-09-15 16:06 UTCGHSA enrichment
  31. 2026-09-15 03:15 UTCEG score recompute
  32. 2026-09-15 03:15 UTCGHSA enrichment
  33. 2026-09-15 03:11 UTCEPSS rescore
  34. 2026-09-14 15:37 UTCGHSA enrichment
  35. 2026-09-14 03:57 UTCEG score recompute
  36. 2026-09-14 03:57 UTCGHSA enrichment
  37. 2026-09-13 16:47 UTCEPSS rescore
  38. 2026-09-13 16:20 UTCGHSA enrichment
  39. 2026-09-13 04:43 UTCGHSA enrichment
  40. 2026-09-12 17:01 UTCEG score recompute
  41. 2026-09-12 17:01 UTCGHSA enrichment
  42. 2026-09-12 05:23 UTCGHSA enrichment
  43. 2026-09-11 17:44 UTCEG score recompute
  44. 2026-09-11 17:44 UTCGHSA enrichment
  45. 2026-09-11 14:53 UTCEPSS rescore
  46. 2026-09-11 05:51 UTCGHSA enrichment
  47. 2026-09-10 18:12 UTCEG score recompute
  48. 2026-09-10 18:12 UTCGHSA enrichment
  49. 2026-09-10 09:35 UTCEPSS rescore
  50. 2026-09-10 06:33 UTCGHSA enrichment
  51. 2026-09-09 18:52 UTCGHSA enrichment
  52. 2026-09-09 06:06 UTCEG score recompute
  53. 2026-09-09 06:06 UTCGHSA enrichment
  54. 2026-09-08 22:01 UTCEPSS rescore
  55. 2026-09-08 07:36 UTCGHSA enrichment
  56. 2026-09-07 17:52 UTCEG score recompute
  57. 2026-09-07 17:52 UTCGHSA enrichment
  58. 2026-09-07 16:01 UTCEPSS rescore
  59. 2026-09-06 15:36 UTCEG score recompute
  60. 2026-09-06 15:36 UTCGHSA enrichment
  61. 2026-09-06 13:47 UTCEPSS rescore
  62. 2026-09-06 03:58 UTCEG score recompute
  63. 2026-09-06 03:58 UTCGHSA enrichment
  64. 2026-09-05 16:21 UTCEG score recompute
  65. 2026-09-05 16:21 UTCGHSA enrichment
  66. 2026-09-05 03:29 UTCEG score recompute
  67. 2026-09-05 03:29 UTCGHSA enrichment
  68. 2026-09-04 09:11 UTCEG score recompute
  69. 2026-09-04 09:11 UTCGHSA enrichment
  70. 2026-09-04 05:07 UTCEPSS rescore
  71. 2026-09-03 17:50 UTCGHSA enrichment
  72. 2026-09-03 06:12 UTCEG score recompute
  73. 2026-09-03 06:12 UTCGHSA enrichment
  74. 2026-09-02 14:12 UTCEPSS rescore
  75. 2026-09-02 06:56 UTCGHSA enrichment

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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 on August 6, 2026, with the most recent update on September 16, 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 0.3% probability of exploitation in the next 30 days (19th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-5856?
CVE-2026-5856 has a CVSS base score of 7.1 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-5856?
An upstream fix for CVE-2026-5856 has been merged but is not yet in a tagged release. Until it ships, restrict network exposure of the affected system or apply the vendor's mitigation, then update to the release that contains the fix. The vendor advisories EchelonGraph has for CVE-2026-5856 are linked in the Vendor Advisories panel on this page.

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