CVE-2018-21263Network attack vector

Authenticated account takeover via crafted SAML response

Published Jun 19, 2020 · Updated Aug 5, 2024

Authentication bypass in Mattermost Server before 4.7.0, 4.6.2, and 4.5.2 allows remote authenticated users to access another account. The SAML authentication flow accepts a crafted response as identity proof for a different Mattermost user; public sources do not disclose the faulty validation step. The flaw is reachable only when SAML authentication is enabled; low-privileged access is sufficient, and successful abuse grants the target account's permissions.

CVSS severity8.8
High
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Mattermost Server before 4.7.0, 4.6.2, and 4.5.2 allows remote authenticated users to access another account. The SAML authentication flow accepts a crafted response as identity proof for a different Mattermost user; public sources do not disclose the faulty validation step. The flaw is reachable only when SAML authentication is enabled; low-privileged access is sufficient, and successful abuse grants the target account's permissions.

The record

CVE
CVE-2018-21263
Published
Jun 19, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-287, T1606.002
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 19, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
T1606.002Forge Web Credentials: SAML Tokens

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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