Mattermost up to 10.11.13/11.5.1 Slash Command server-side request forgery

CVSS Meta Temp Score
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CTI Interest Score
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4.4$0-$5k0.00

Summaryinfo

A vulnerability labeled as critical has been found in Mattermost up to 10.11.13/11.5.1. The affected element is an unknown function of the component Slash Command Handler. The manipulation results in server-side request forgery. This vulnerability was named CVE-2026-6333. The attack may be performed from remote. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as critical, was found in Mattermost up to 10.11.13/11.5.1. Affected is an unknown part of the component Slash Command Handler. The manipulation with an unknown input leads to a server-side request forgery vulnerability. CWE is classifying the issue as CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate the Host header when constructing response URLs for custom slash commands which allows an authenticated attacker to redirect slash command responses to an attacker-controlled server via a spoofed Host header.. Mattermost Advisory ID: MMSA-2026-00582

The weakness was presented by Juho Forsén. The advisory is available at mattermost.com. This vulnerability is traded as CVE-2026-6333 since 04/15/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The technical details are unknown and an exploit is not available.

The vulnerability scanner Nessus provides a plugin with the ID 316489 (Mattermost Server 10.11.x <= 10.11.13 / 11.5.x <= 11.5.1 Multiple Vulnerabilities (MMSA-2026-00570 / MMSA-2026-00575 / MMSA-2026-00582 / MMSA-2026-00622)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 10.11.14, 11.5.2 or 11.6.0 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (316489) and EUVD (EUVD-2026-30755). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

Name

Version

License

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.5
VulDB Meta Temp Score: 4.4

VulDB Base Score: 5.0
VulDB Temp Score: 4.8
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.0
NVD Vector: 🔒

CNA Base Score: 3.5
CNA Vector (Mattermost): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Server-side request forgery
CWE: CWE-918
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 316489
Nessus Name: Mattermost Server 10.11.x <= 10.11.13 / 11.5.x <= 11.5.1 Multiple Vulnerabilities (MMSA-2026-00570 / MMSA-2026-00575 / MMSA-2026-00582 / MMSA-2026-00622)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Mattermost 10.11.14/11.5.2/11.6.0

Timelineinfo

04/15/2026 CVE reserved
05/18/2026 +33 days Advisory disclosed
05/18/2026 +0 days VulDB entry created
05/23/2026 +5 days VulDB entry last update

Sourcesinfo

Advisory: mattermost.com
Researcher: Juho Forsén
Status: Confirmed

CVE: CVE-2026-6333 (🔒)
GCVE (CVE): GCVE-0-2026-6333
GCVE (VulDB): GCVE-100-364458
EUVD: 🔒

Entryinfo

Created: 05/18/2026 12:25
Updated: 05/23/2026 14:48
Changes: 05/18/2026 12:25 (65), 05/18/2026 15:34 (1), 05/23/2026 07:33 (11), 05/23/2026 14:48 (2)
Complete: 🔍
Cache ID: 216::103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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