CVE-2018-21251

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit probability: 1.2% (66th percentile of EPSS-scored CVEs). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
9.8EG
EchelonGraph verdictPlan mitigationSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1.2%CVSS: 9.8Exploit: None knownExposed services: Not assessed

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

An issue was discovered in Mattermost Server before 5.2 and 5.1.1. Authorization could be bypassed if the channel name were not the same in the params and the body.

CVSS v3
9.8
EG Score
9.8CRITICALmedium confidence
EG Risk
49
EG Risk 49/100CISA 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
Severity98% × 45%
Exploitation1% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track* or Attend at high (mission-essential systems).
Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.
EPSS PROB
1.2%
EPSS %ILE
67th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* or Attend at high (mission-essential systems).

No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.

Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact total (CVSS ≥ 9.0). 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

June 19, 2020

Last Modified

November 21, 2024

Advisory Details (1)

Auto-updated Oct 6, 2026
No fix on record yet.
generic

Security Updates | Mattermost Documentation

https://mattermost.com/security-updates/

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 25× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 89 of 157 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 11 repeat rows among the latest 100 are merged into the row they repeat. The 68 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-10 19:55 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  2. 2026-10-09 20:02 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  3. 2026-10-08 16:36 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  4. 2026-10-07 23:42 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  5. 2026-10-06 15:12 UTCEPSS rescoreEPSS 1.2% · 67th percentile
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  7. 2026-10-04 23:18 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  8. 2026-10-03 14:21 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  9. 2026-10-01 19:44 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  10. 2026-09-30 14:59 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  11. 2026-09-30 10:00 UTCEG score recompute
  12. 2026-09-28 13:45 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  13. 2026-09-27 13:40 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  14. 2026-09-26 22:41 UTCOSV refresh
  15. 2026-09-26 15:53 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  16. 2026-09-24 13:59 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  17. 2026-09-20 20:10 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  18. 2026-09-19 15:36 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  19. 2026-09-18 19:22 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  20. 2026-09-17 19:22 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  21. 2026-09-16 05:06 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  22. 2026-09-15 03:05 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  23. 2026-09-13 16:42 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  24. 2026-09-12 14:56 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  25. 2026-09-11 14:47 UTCEPSS rescoreEPSS 1.2% · 66th percentile
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  1. 2026-09-11 09:32 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  2. 2026-09-07 15:57 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  3. 2026-09-07 08:18 UTCOSV refresh
  4. 2026-09-06 13:43 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  5. 2026-09-05 15:24 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  6. 2026-09-04 13:56 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  7. 2026-09-04 05:02 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  8. 2026-09-02 14:07 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  9. 2026-09-01 13:49 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  10. 2026-09-01 03:32 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  11. 2026-08-28 21:36 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  12. 2026-08-27 14:21 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  13. 2026-08-26 14:42 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  14. 2026-08-25 13:44 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  15. 2026-08-21 23:45 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  16. 2026-08-20 22:51 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  17. 2026-08-20 18:01 UTCOSV refresh
  18. 2026-08-19 17:00 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  19. 2026-08-18 13:44 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  20. 2026-08-17 13:43 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  21. 2026-08-16 14:51 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  22. 2026-08-16 02:10 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  23. 2026-08-15 01:26 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  24. 2026-08-13 21:56 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  25. 2026-08-12 13:46 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  26. 2026-08-09 13:43 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  27. 2026-08-08 16:32 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  28. 2026-08-07 16:23 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  29. 2026-08-06 13:42 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  30. 2026-08-05 19:13 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  31. 2026-08-05 11:41 UTCOSV refresh
  32. 2026-08-04 15:05 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  33. 2026-08-02 02:23 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  34. 2026-08-01 04:12 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  35. 2026-07-30 16:24 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  36. 2026-07-30 01:27 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  37. 2026-07-28 15:32 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  38. 2026-07-26 14:51 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  39. 2026-07-25 14:14 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  40. 2026-07-23 14:15 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  41. 2026-07-23 01:35 UTCEG score recompute
  42. 2026-07-22 22:15 UTCEG score recompute
  43. 2026-07-22 14:05 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  44. 2026-07-21 15:22 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  45. 2026-07-20 17:04 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  46. 2026-07-19 14:28 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  47. 2026-07-19 10:52 UTCOSV refresh
  48. 2026-07-19 02:26 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  49. 2026-07-16 16:59 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  50. 2026-07-15 16:55 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  51. 2026-07-15 01:56 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  52. 2026-07-13 22:26 UTCEPSS rescoreEPSS 1.2% · 64th percentile
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  54. 2026-07-11 08:24 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  55. 2026-07-09 19:06 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  56. 2026-07-08 15:11 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  57. 2026-07-07 13:42 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  58. 2026-07-06 16:24 UTCEPSS rescoreEPSS 1.2% · 64th percentile
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  61. 2026-07-04 06:28 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  62. 2026-07-02 16:54 UTCEPSS rescoreEPSS 1.2% · 64th percentile
  63. 2026-07-01 17:31 UTCOSV refresh
  64. 2026-07-01 15:03 UTCEPSS rescoreEPSS 1.2% · 64th percentile

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Frequently asked(5)

What is CVE-2018-21251?
CVE-2018-21251 is a critical vulnerability published on June 19, 2020. An issue was discovered in Mattermost Server before 5.2 and 5.1.1. Authorization could be bypassed if the channel name were not the same in the params and the body.
When was the CVE record for CVE-2018-21251 published?
The CVE record for CVE-2018-21251 was published on June 19, 2020. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of November 21, 2024; the record at its source may have been updated since.
Is CVE-2018-21251 actively exploited?
CVE-2018-21251 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.2% probability of exploitation in the next 30 days (67th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2018-21251?
CVE-2018-21251 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2018-21251?
No fix for CVE-2018-21251 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix.

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