CVE-2018-21264Network attack vector

Authentication beyond assertion expiry via missing SAML validation

Published Jun 19, 2020 · Updated Aug 5, 2024

Improper SAML response validation in Mattermost Server before 4.7.0, 4.6.2, and 4.5.2 allows remote authenticated users to reuse expired responses. The SAML sign-in path accepts a response after its embedded expiration date instead of rejecting the stale authentication assertion. Exposure requires SAML authentication and possession of a previously valid response, extending account access beyond the identity provider's intended lifetime.

CVSS severity8.8
High
EPSS probability1.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper SAML response validation in Mattermost Server before 4.7.0, 4.6.2, and 4.5.2 allows remote authenticated users to reuse expired responses. The SAML sign-in path accepts a response after its embedded expiration date instead of rejecting the stale authentication assertion. Exposure requires SAML authentication and possession of a previously valid response, extending account access beyond the identity provider's intended lifetime.

The record

CVE
CVE-2018-21264
Published
Jun 19, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, T1078
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.

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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
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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