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CVE-2026-12985— Mattermost DCR redirect URI allowlist bypass via improper URL component validation

Quick assessment

Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mattermost是美国Mattermost公司开源的一个开源协作平台。 Mattermost 11.9.0及之前的11.9.x版本、11.8.4及之前的11.8.x版本和11.7.7及之前的11.7.x版本存在输入验证错误漏洞，该漏洞源于未能按URL组件验证动态客户端注册重定向URI，而是将glob模式与原始URI字符串进行匹配，可能导致远程未经身份验证的攻击者注册OAuth客户端，并通过特制重定向URI绕过配置的重定向URI允许列表，从而使用攻击者控制的回调主机。

CVSS 6.8 · Medium EPSS 0.27% · P19

Affected Version Matrix 7

VendorProduct Version RangeStatus
Mattermost Mattermost 11.9.0≤ 11.9.0 affected
11.8.0≤ 11.8.4 affected
11.7.0≤ 11.7.7 affected
11.10.0 unaffected
11.9.1 unaffected
11.8.5 unaffected
11.7.8 unaffected
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I. Basic Information for CVE-2026-12985

Vulnerability Information
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Vulnerability Title
Mattermost DCR redirect URI allowlist bypass via improper URL component validation
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 Mattermost failed to validate Dynamic Client Registration redirect URIs by URL component (matching glob patterns against the raw URI string instead) which allows a remote unauthenticated attacker to register an OAuth client with an attacker-controlled callback host that bypasses the configured redirect URI allowlist via a crafted redirect URI that places an allowlisted host/path suffix inside the query string.. Mattermost Advisory ID: MMSA-2026-00700
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
指向未可信站点的URL重定向(开放重定向)
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司开源的一个开源协作平台。 Mattermost 11.9.0及之前的11.9.x版本、11.8.4及之前的11.8.x版本和11.7.7及之前的11.7.x版本存在输入验证错误漏洞，该漏洞源于未能按URL组件验证动态客户端注册重定向URI，而是将glob模式与原始URI字符串进行匹配，可能导致远程未经身份验证的攻击者注册OAuth客户端，并通过特制重定向URI绕过配置的重定向URI允许列表，从而使用攻击者控制的回调主机。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Mattermost Mattermost 11.9.0 ~ 11.9.0 -

II. Public POCs for CVE-2026-12985

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III. Intelligence Information for CVE-2026-12985

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Same Patch Batch · Mattermost · 2026-09-14 · 16 CVEs total

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CVE-2026-5132 6.5 MEDIUM Unbounded zlib decompression in Calls SDP WebSocket messages
CVE-2026-91181 6.5 MEDIUM Data Retention Teams Endpoint Leaks Private Team Invite ID
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CVE-2026-10556 5.3 MEDIUM Unauthenticated webhook request with null notification entry could crash the Microsoft Cal
CVE-2026-10542 5.0 MEDIUM Playbooks channel action update validation issue
CVE-2026-11993 4.3 MEDIUM Fix authenticated members disabling file content indexing server-wide via extraction pool
CVE-2026-14344 4.3 MEDIUM Inconsistent authorization checks in Mattermost Boards endpoints
CVE-2026-14259 4.3 MEDIUM Board archive import bypasses team board creation permissions
CVE-2026-12882 4.3 MEDIUM Mattermost Markdown autolink parsing denial of service
CVE-2026-13417 4.3 MEDIUM Boards plugin denial of service via unvalidated block fields.properties
CVE-2026-86348 4.3 MEDIUM MS Calendar plugin: unrecovered handler panics from malformed post-action requests could c
CVE-2026-86349 4.3 MEDIUM Mattermost Server Algorithmic DoS via Unbounded Markdown Block Nesting

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-601