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CVE-2026-3495— Unescaped variables during error page composition

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公司的一个开源协作平台。 Mattermost 11.5.1及之前的11.5.x版本和10.11.13及之前的10.11.x版本存在跨站脚本漏洞，该漏洞源于错误页面组合时未转义可能包含恶意内容的变量，可能导致具有编辑站点配置权限的攻击者通过注入JS执行恶意代码。

CVSS 3.8 · Low EPSS 0.24% · P14

Affected Version Matrix 5

VendorProduct Version RangeStatus
Mattermost Mattermost 11.5.0≤ 11.5.1 affected
10.11.0≤ 10.11.13 affected
11.6.0 unaffected
11.5.2 unaffected
10.11.14 unaffected
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I. Basic Information for CVE-2026-3495

Vulnerability Information
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Vulnerability Title
Unescaped variables during error page composition
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to escape some variables that could contain malicious content during error page composition which allows an attacker with access to edit some site configuration to execute some malicious code via injecting some JS as part of those values.. Mattermost Advisory ID: MMSA-2026-00622
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.5.1及之前的11.5.x版本和10.11.13及之前的10.11.x版本存在跨站脚本漏洞，该漏洞源于错误页面组合时未转义可能包含恶意内容的变量，可能导致具有编辑站点配置权限的攻击者通过注入JS执行恶意代码。
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 11.5.0 ~ 11.5.1 -

II. Public POCs for CVE-2026-3495

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III. Intelligence Information for CVE-2026-3495

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Same Patch Batch · Mattermost · 2026-05-18 · 21 CVEs total

CVE-2026-6346 8.7 HIGH Sensitive credentials exposed in plaintext in Mattermost support packets
CVE-2026-6347 7.6 HIGH Mattermost Calls plugin exposes TURN server credentials in plaintext in support packets
CVE-2026-6345 6.5 MEDIUM Prevent password disclosure and force reset during Slack import
CVE-2026-5163 6.5 MEDIUM Missing authorization check in AI message rewrite endpoint allows access to private thread
CVE-2026-3117 6.5 MEDIUM Instance and webhook GitLab plugin commands were able to be run by non-admin users
CVE-2026-3471 6.5 MEDIUM Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop
CVE-2026-28759 4.3 MEDIUM Insufficient authorization in shared channel membership sync allows remote cluster to remo
CVE-2026-2325 4.3 MEDIUM Improper Input Validation in MS Teams Meetings API Handler
CVE-2026-3637 4.3 MEDIUM Mattermost fails to enforce create_post permission when editing posts
CVE-2026-6342 4.3 MEDIUM Group prefix matching bypass for subscriptions
CVE-2026-6341 4.3 MEDIUM Incomplete group locking implementation
CVE-2026-6340 4.3 MEDIUM Memory Exhaustion via Malicious 7zip File Upload
CVE-2026-6339 4.3 MEDIUM Missing request origin validation on burn-on-read reveal endpoint
CVE-2026-6343 4.3 MEDIUM Mattermost Playbooks Plugin fails to enforce view permissions in list endpoints, allowing
CVE-2026-28732 4.3 MEDIUM Slash command trigger-word update allowed command hijacking
CVE-2026-4273 3.7 LOW Insufficient token rotation validation in remote cluster invite confirmation
CVE-2026-6333 3.5 LOW SSRF via Host Header Spoofing in Custom Slash Commands
CVE-2026-4643 3.5 LOW Calling window.close() from server-side content causes crash in the Mattermost Desktop App
CVE-2026-6334 3.1 LOW OAuth authorization code client binding not enforced during token redemption in Mattermost
CVE-2026-4286 3.1 LOW Playbooks Plugin fails to validate team transfers, allowing unauthorized removal of member

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-79

V. Comments for CVE-2026-3495

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