Medium severity · published Apr 9, 2026
CVE-2026-21388
Unbounded Request Body Read in MS Teams Plugin {{/lifecycle}} Webhook Endpoint
6.5
CVSS
0.3%
EPSS
No
On KEV
Description
Mattermost Plugins versions <=2.3.1 fail to limit the request body size on the {{/lifecycle}} webhook endpoint which allows an authenticated attacker to cause memory exhaustion and denial of service via sending an oversized JSON payload. Mattermost Advisory ID: MMSA-2026-00610
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 24% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
through 2.3.1 · source: vendor
MS
Mattermost Server · Mattermost
through 2.3.1 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-21388
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-21388
Vendor Advisory
https://mattermost.com/security-updates
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