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CVE-2026-28735

MEDIUMCVSS 5.4/10EPSS 0.14%

Last modified

CVE-2026-28735 is a medium-severity vulnerability rated 5.4/10 on the CVSS scale. Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628. EPSS estimates a 0.14% chance of exploitation in the next 30 days.

Description

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628

Metrics

CVSS 3.1
5.4/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

EPSS Probability
0.14%

3.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
MattermostMattermost Server>= 10.11.0, < 10.11.15
MattermostMattermost Server>= 11.4.0, < 11.4.5
MattermostMattermost Server>= 11.5.0, < 11.5.4
MattermostMattermost Server>= 11.6.0, < 11.6.1

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-28735?
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628
How severe is CVE-2026-28735?
CVE-2026-28735 has a CVSS score of 5.4/10 (MEDIUM severity). The EPSS model estimates a 0.14% probability of exploitation in the next 30 days.
How do I fix CVE-2026-28735?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-28735?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST