CVE-2026-28759

MEDIUMNVD 4.34.3—
EchelonGraph scoreMEDIUM confidence

Score 4.3 from GitHub Security Advisory published 2026-05-18. NVD baseline CVSS 4.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
4.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 4.3Exploit: NoneExposed: 0

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

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576

CVSS v3
4.3
EG Score
4.3(medium)
EPSS
4.8%
KEV
Not listed

Published

May 18, 2026

Last Modified

May 18, 2026

Advisory Details (1)

Auto-updated May 18, 2026
No patch confirmed yet.
generic

Security Updates

https://mattermost.com/security-updates

Vendor Advisories for CVE-2026-28759(1)

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

Affected Packages

(2 across 1 ecosystem)
Go(2)
PackageVulnerable rangeFixed inDependents
github.com/mattermost/mattermost-server—5.3.2-0.20260216150504-8738f8c4b3d4—
github.com/mattermost/mattermost/server/v8—8.0.0-20260216150504-8738f8c4b3d4—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 8× in last 7d / 52× 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 113 total refreshes for this CVE.

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

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-28759?
CVE-2026-28759 is a medium vulnerability published on May 18, 2026. Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any…
When was CVE-2026-28759 disclosed?
CVE-2026-28759 was first published in the National Vulnerability Database on May 18, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-28759 actively exploited?
CVE-2026-28759 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 4.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-28759?
CVE-2026-28759 has a CVSS v3 base score of 4.3 (NVD).
How do I remediate CVE-2026-28759?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-28759, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-28759

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