CVE-2026-28736
CVE-2026-28736 is a medium-severity vulnerability in Mattermost Focalboard with a CVSS 3.x base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-639.
Key facts
- Severity: Medium (CVSS 3.x base score 4.3)
- EPSS exploit prediction: 0% (13th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-18653
- Weakness: CWE-639
- Affected product: Mattermost Focalboard
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-28736?
- ** 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.
- How severe is CVE-2026-28736?
- CVE-2026-28736 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
- Is CVE-2026-28736 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-28736?
- CVE-2026-28736 affects Mattermost Focalboard. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-28736?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-28736 have an EU (EUVD) identifier?
- Yes. CVE-2026-28736 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18653.
- When was CVE-2026-28736 published?
- CVE-2026-28736 was published on 2026-04-03 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:a:mattermost:focalboard:8.0.0:*:*:*:*:*:*:*
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