CVE-2026-6340

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 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted 7zip file with excessive folder declarations.. Mattermost Advisory ID: MMSA-2026-00573

CVSS v3
4.3
EG Score
4.3(medium)
EPSS
15.0%
KEV
Not listed

Published

May 18, 2026

Last Modified

May 19, 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-2026-6340(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—5.3.2-0.20260325191733-fb11968f8798—
github.com/mattermost/mattermost/server/v8—8.0.0-20260325191733-fb11968f8798—

Weakness Classification(1)

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

Data Freshness Timeline

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

Frequently asked(5)

What is CVE-2026-6340?
CVE-2026-6340 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 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted 7zip file with excessive folder…
When was CVE-2026-6340 disclosed?
CVE-2026-6340 was first published in the National Vulnerability Database on May 18, 2026, with the most recent update on May 19, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-6340 actively exploited?
CVE-2026-6340 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 15.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-6340?
CVE-2026-6340 has a CVSS v3 base score of 4.3 (NVD).
How do I remediate CVE-2026-6340?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-6340, 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-2026-6340

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