CVE-2021-37863Network attack vector

Client-side crash via malformed post parameters

Published Dec 17, 2021 · Updated Aug 4, 2024

Improper input validation in Mattermost 6.0 and earlier allows remote authenticated users to crash a web client with a malicious post. The post-creation path accepts maliciously crafted parameters that the web application cannot process safely; Mattermost has not disclosed the specific parameter or client parsing locus. An attacker needs a valid account, and a victim must render the crafted post; the reported consequence is limited to a client-side crash.

CVSS severity3.5
Low
EPSS probability0.83%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Mattermost 6.0 and earlier allows remote authenticated users to crash a web client with a malicious post. The post-creation path accepts maliciously crafted parameters that the web application cannot process safely; Mattermost has not disclosed the specific parameter or client parsing locus. An attacker needs a valid account, and a victim must render the crafted post; the reported consequence is limited to a client-side crash.

The record

CVE
CVE-2021-37863
Published
Dec 17, 2021
Updated
Aug 4, 2024
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=unspecified <=6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=unspecified <=6.0

Published CVSS scores

5.7NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
3.5Mattermost, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:L
3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:N/A:P

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-20Improper Input Validation
T1499.004Application or System Exploitation

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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