CVE-2026-21388Network attack vector

Service interruption via unbounded lifecycle webhook body

Published Apr 9, 2026 · Updated Apr 9, 2026

Resource exhaustion in Mattermost MS Teams plugin 2.3.1 and earlier allows remote authenticated users to interrupt service. The processLifecycle handler passes the uncapped lifecycle webhook body to JSON decoding, so an oversized payload consumes server memory. Authenticated access to that endpoint is required; an oversized request can exhaust available memory and interrupt service.

CVSS severity3.7
Low
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Mattermost MS Teams plugin 2.3.1 and earlier allows remote authenticated users to interrupt service. The processLifecycle handler passes the uncapped lifecycle webhook body to JSON decoding, so an oversized payload consumes server memory. Authenticated access to that endpoint is required; an oversized request can exhaust available memory and interrupt service.

The record

CVE
CVE-2026-21388
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-770, T1499.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=2.3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=0 <=2.3.1

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.7Mattermost, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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