User-Agent Header Vulnerability in Mattermost by Mattermost
CVE-2026-25783

4.3MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
16 March 2026

What is CVE-2026-25783?

Certain versions of Mattermost, including 11.3.x, 11.2.x, and 10.11.x, exhibit a security flaw where the User-Agent header tokens are not validated correctly. This vulnerability allows an authenticated attacker to exploit this oversight by sending a specially crafted User-Agent header, which can result in a request panic. Organizations using these affected versions should assess their systems to mitigate any potential risks associated with this vulnerability. Additional details can be found in the Mattermost Advisory.

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Affected Version(s)

Mattermost 11.3.0

Mattermost 11.2.0 <= 11.2.2

Mattermost 10.11.0 <= 10.11.10

References

https://mattermost.com/security-updates
vendor-advisory

CVSS V3.1

Score:
4.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

winfunc
JSON
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