MEDIUM
CVE-2026-28735
CWE-863Published: May 22, 2026· Updated: May 22, 2026
5.4
CVSS v3.1
EPSS:0.03%probability of exploitation in 30 daysPercentile:7.4th
Official 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
Technical Analysis
CVE-2026-28735 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.
Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CVSS v3.1 Vector Breakdown
Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.Low
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityLow
IntegrityLow
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Affected Vendors & Products
mattermost1 product
mattermost server
Source: NVD CPE · 1 total CPE entries
Exploit & PoC Resources
NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.
Official Patches & Advisories
All References (1)
→
https://mattermost.com/security-updatesVendor Advisory
Quick Facts
CVE IDCVE-2026-28735
CVSS Score5.4 / 10
SeverityMEDIUM
WeaknessCWE-863
CISA KEVNo
EPSS (30d)0.03%
Affected1 vendor
PublishedMay 22, 2026
Related CVEs (CWE-863)
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2026-28735 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.