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VulnerabilityPublished

CVE-2026-28736: Mattermost Focalboard · Insecure Direct Object Reference

Affects Mattermost FocalboardSource CVE Database V5

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Not known to be exploited · CVSS 4.3 Medium · end of life, no fix coming : replace or isolate Mattermost Focalboard; no fix will be released.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
4.3Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 12% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
None coming – the product is end of life
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 3 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

No fix will be released: Mattermost Focalboard is end of life. Replace it, or isolate it from untrusted networks until you can.

Affected software

ProductAffectedFixed in
MattermostFocalboardAffected
  • <=8.0
Fixed in–
GitHubmattermost-community/focalboardpkg:github/mattermost-community/focalboardOther threatsAffected
  • =0
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Users should consider discontinuing use of the vulnerable version or migrating to alternative solutions. Restricting access to the application and limiting knowledge of fileIDs may reduce risk but do not fully mitigate the vulnerability. Monitor for any updates from Mattermost regarding this issue.

Description

** UNSUPPORTED WHEN ASSIGNED ** Focalboard version 8.0 fails to validate file ownership when serving uploaded files. This allows an authenticated attacker who knows a victim's fileID to read the content of the file. NOTE: Focalboard as a standalone product is not maintained and no fix will be issued.

References

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