CVE-2026-5857

HIGHPre-NVD 8.18.1—
EchelonGraph scoreHIGH confidence

Score 8.1 from GitHub Security Advisory (severity: CRITICAL) published 2026-08-07. the CNA's CVSS baseline 8.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cna:vulncheck, epss, ghsa
Trending — 3 sources updated this week
8.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 8.1Exploit: None knownExposed: 0

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

Contiki-NG's MQTT client parse_publish_vhdr() in os/net/app-layer/mqtt/mqtt.c sets topic_len_received=1 before checking topic_len against the 64-byte limit, so an over-length topic returns early but leaves the flag set. On the next TCP segment, tcp_input() re-invokes the parser with topic_received==0, and the persisted topic_len_received==1 skips the length-reading block containing the guard, falling through directly to a memcpy() that uses the unvalidated 16-bit topic_len as the copy length. The 65-byte topic[] destination overruns into adjacent struct fields including the payload_chunk pointer, which subsequent MQTT code dereferences, giving a compromised or attacker-controlled broker an arbitrary-pointer-write primitive. Contiki-NG's MQTT implementation has no TLS support so the connection is plaintext. Impact ranges from information disclosure and denial of service to remote code execution on embedded targets without memory protection.

CVSS v3
8.1
EG Score
8.1(high)
EG Risk
52(Track)
EG Risk 52/100SSVC: 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
Severity81% × 45%
Exploitation1% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
43%
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_pr, github_commit.
github_commit

commit a34a2dbdc8be (contiki-ng/contiki-ng)

Fix landed in contiki-ng/contiki-ng commit a34a2dbdc8be — awaiting tagged release

https://github.com/contiki-ng/contiki-ng/commit/a34a2dbdc8bea784bd2ae5079aa4be520cd74f2d
github_pr

mqtt: harden TCP input parsing against malformed and coalesced packets

Fix merged in contiki-ng/contiki-ng PR #3163 on 2026-07-10 — awaiting tagged release

https://github.com/contiki-ng/contiki-ng/pull/3163
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-2026-5857(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 28× in last 7d / 66× 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 01:53 UTCEG score recompute
  2. 2026-08-21 01:53 UTCGHSA enrichment
  3. 2026-08-20 22:55 UTCEPSS rescore
  4. 2026-08-20 14:19 UTCGHSA enrichment
  5. 2026-08-20 02:21 UTCEG score recompute
  6. 2026-08-20 02:21 UTCGHSA enrichment
  7. 2026-08-19 17:04 UTCEPSS rescore
  8. 2026-08-19 14:49 UTCGHSA enrichment
  9. 2026-08-19 03:16 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 01:55 UTCGHSA enrichment
  14. 2026-08-17 14:23 UTCEG score recompute
  15. 2026-08-17 14:23 UTCGHSA enrichment
  16. 2026-08-17 13:47 UTCEPSS rescore
  17. 2026-08-17 02:51 UTCGHSA enrichment
  18. 2026-08-16 15:19 UTCEG score recompute
  19. 2026-08-16 15:19 UTCGHSA enrichment
  20. 2026-08-16 14:56 UTCEPSS rescore
  21. 2026-08-16 03:47 UTCEG score recompute
  22. 2026-08-16 03:47 UTCGHSA enrichment
  23. 2026-08-15 16:15 UTCGHSA enrichment
  24. 2026-08-15 04:43 UTCEG score recompute
  25. 2026-08-15 04:43 UTCGHSA enrichment
Show 41 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 08:55 UTCEG score recompute
  5. 2026-08-14 08:55 UTCGHSA enrichment
  6. 2026-08-13 22:00 UTCEPSS rescore
  7. 2026-08-13 21:23 UTCEG score recompute
  8. 2026-08-13 21:23 UTCGHSA enrichment
  9. 2026-08-13 20:38 UTCEG score recompute
  10. 2026-08-13 20:38 UTCGHSA enrichment
  11. 2026-08-13 10:12 UTCGHSA enrichment
  12. 2026-08-12 22:40 UTCEG score recompute
  13. 2026-08-12 22:40 UTCGHSA enrichment
  14. 2026-08-12 13:51 UTCEPSS rescore
  15. 2026-08-12 11:09 UTCGHSA enrichment
  16. 2026-08-11 23:36 UTCEG score recompute
  17. 2026-08-11 23:36 UTCGHSA enrichment
  18. 2026-08-11 12:05 UTCGHSA enrichment
  19. 2026-08-11 00:33 UTCEG score recompute
  20. 2026-08-11 00:33 UTCGHSA enrichment
  21. 2026-08-11 00:00 UTCEPSS rescore
  22. 2026-08-10 13:01 UTCGHSA enrichment
  23. 2026-08-10 01:29 UTCGHSA enrichment
  24. 2026-08-09 13:57 UTCEG score recompute
  25. 2026-08-09 13:57 UTCGHSA enrichment
  26. 2026-08-09 13:46 UTCEPSS rescore
  27. 2026-08-09 02:26 UTCEG score recompute
  28. 2026-08-09 02:26 UTCGHSA enrichment
  29. 2026-08-08 16:37 UTCEPSS rescore
  30. 2026-08-08 14:54 UTCGHSA enrichment
  31. 2026-08-08 03:22 UTCEG score recompute
  32. 2026-08-08 03:22 UTCGHSA enrichment
  33. 2026-08-08 02:52 UTCEG score recompute
  34. 2026-08-08 02:52 UTCGHSA enrichment
  35. 2026-08-07 21:25 UTCEG score recompute
  36. 2026-08-07 21:25 UTCGHSA enrichment
  37. 2026-08-07 09:53 UTCEG score recompute
  38. 2026-08-07 09:53 UTCGHSA enrichment
  39. 2026-08-06 22:22 UTCEG score recompute
  40. 2026-08-06 22:16 UTCEG score recompute
  41. 2026-08-06 22:15 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-5857?
CVE-2026-5857 is a high vulnerability published on August 6, 2026. Contiki-NG's MQTT client parsepublishvhdr() in os/net/app-layer/mqtt/mqtt.c sets topiclenreceived=1 before checking topiclen against the 64-byte limit, so an over-length topic returns early but leaves the flag set. On the next TCP segment, tcpinput() re-invokes the parser with topicreceived==0, and…
When was CVE-2026-5857 disclosed?
CVE-2026-5857 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-2026-5857 actively exploited?
CVE-2026-5857 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 57.0% of all scored CVEs.
What is the CVSS score of CVE-2026-5857?
CVE-2026-5857 has a CVSS v4.0 base score of 8.1 (CNA self-assessment; NVD's own analysis pending).
How do I remediate CVE-2026-5857?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-5857, 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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