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
4.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 4.3Exploit: None knownExposed: 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)
EG Risk
19(Track)
EG Risk 19/100SSVC: 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
Severity43% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
15%
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

(4 across 1 ecosystem)
Go(4)
PackageVulnerable rangeFixed inDependents
github.com/mattermost/mattermost-server—11.5.2+incompatible—
github.com/mattermost/mattermost-server/v5———
github.com/mattermost/mattermost-server/v6———
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 8× in last 7d / 46× 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 146 total refreshes for this CVE.

  1. 2026-08-25 13:49 UTCEPSS rescore
  2. 2026-08-23 17:17 UTCEG score recompute
  3. 2026-08-23 00:19 UTCEPSS rescore
  4. 2026-08-22 00:40 UTCEG score recompute
  5. 2026-08-21 23:49 UTCEPSS rescore
  6. 2026-08-20 22:56 UTCEPSS rescore
  7. 2026-08-20 19:11 UTCEG score recompute
  8. 2026-08-19 17:04 UTCEPSS rescore
  9. 2026-08-18 13:49 UTCEPSS rescore
  10. 2026-08-18 13:49 UTCEPSS rescore
  11. 2026-08-17 13:47 UTCEPSS rescore
  12. 2026-08-17 10:08 UTCEG score recompute
  13. 2026-08-16 14:56 UTCEPSS rescore
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  15. 2026-08-16 03:41 UTCEG score recompute
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  18. 2026-08-14 02:14 UTCEG score recompute
  19. 2026-08-13 22:00 UTCEPSS rescore
  20. 2026-08-12 22:27 UTCEG score recompute
  21. 2026-08-12 13:51 UTCEPSS rescore
  22. 2026-08-11 23:35 UTCEG score recompute
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  25. 2026-08-10 00:33 UTCEG score recompute
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  1. 2026-08-09 13:47 UTCEPSS rescore
  2. 2026-08-09 01:41 UTCEG score recompute
  3. 2026-08-08 16:37 UTCEPSS rescore
  4. 2026-08-07 19:10 UTCEG score recompute
  5. 2026-08-06 20:18 UTCEG score recompute
  6. 2026-08-06 13:47 UTCEPSS rescore
  7. 2026-08-05 21:26 UTCEG score recompute
  8. 2026-08-05 19:17 UTCEPSS rescore
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  10. 2026-08-04 15:10 UTCEPSS rescore
  11. 2026-08-04 10:39 UTCEPSS rescore
  12. 2026-08-03 17:08 UTCEG score recompute
  13. 2026-08-03 10:36 UTCEPSS rescore
  14. 2026-08-02 17:30 UTCEG score recompute
  15. 2026-08-02 02:27 UTCEPSS rescore
  16. 2026-08-01 18:38 UTCEG score recompute
  17. 2026-08-01 04:16 UTCEPSS rescore
  18. 2026-07-30 16:28 UTCEPSS rescore
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  20. 2026-07-28 15:37 UTCEPSS rescore
  21. 2026-07-27 14:14 UTCEPSS rescore
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  24. 2026-07-25 14:18 UTCEPSS rescore
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  27. 2026-07-24 14:18 UTCEPSS rescore
  28. 2026-07-23 14:18 UTCEPSS rescore
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  30. 2026-07-23 03:22 UTCEG score recompute
  31. 2026-07-22 14:08 UTCEPSS rescore
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  33. 2026-07-21 15:25 UTCEPSS rescore
  34. 2026-07-21 15:25 UTCEPSS rescore
  35. 2026-07-20 17:08 UTCEPSS rescore
  36. 2026-07-19 14:31 UTCEPSS rescore
  37. 2026-07-19 02:29 UTCEPSS rescore
  38. 2026-07-18 10:04 UTCEPSS rescore
  39. 2026-07-18 00:29 UTCOSV refresh
  40. 2026-07-16 17:03 UTCEPSS rescore
  41. 2026-07-15 16:57 UTCEPSS rescore
  42. 2026-07-15 02:00 UTCEPSS rescore
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  44. 2026-07-13 22:31 UTCEPSS rescore
  45. 2026-07-13 06:13 UTCEPSS rescore
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  47. 2026-07-12 05:46 UTCEPSS rescore
  48. 2026-07-11 08:27 UTCEPSS rescore
  49. 2026-07-11 08:27 UTCEPSS rescore
  50. 2026-07-09 19:10 UTCEPSS rescore
  51. 2026-07-09 19:10 UTCEPSS rescore
  52. 2026-07-08 15:16 UTCEPSS rescore
  53. 2026-07-08 15:16 UTCEPSS rescore
  54. 2026-07-07 13:46 UTCEPSS rescore
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  56. 2026-07-06 16:27 UTCEPSS rescore
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  65. 2026-06-30 23:22 UTCEPSS rescore
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  67. 2026-06-28 14:07 UTCEPSS rescore
  68. 2026-06-28 04:56 UTCEPSS rescore
  69. 2026-06-27 03:08 UTCEPSS rescore
  70. 2026-06-25 13:50 UTCEPSS rescore
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  72. 2026-06-23 21:33 UTCEPSS rescore
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  74. 2026-06-22 14:25 UTCEPSS rescore
  75. 2026-06-22 14:25 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 0% probability of exploitation in the next 30 days, which ranks it in the top 85.1% of all scored CVEs.
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

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