Unescaped variables during error page composition

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Summary

CVECVE-2026-3495
StatePUBLISHED
AssignerMattermost
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-18 08:16:13 UTC
Updated2026-05-19 17:37:07 UTC
DescriptionMattermost 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

Risk And Classification

Primary CVSS: v3.1 4.8 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N

EPSS: 0.000300000 probability, percentile 0.089100000 (date 2026-05-26)

Problem Types: CWE-79 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary4.8MEDIUMCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
3.1[email protected]Secondary3.8LOWCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N
3.1CNACVSS3.8LOWCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Mattermost Mattermost Server All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mattermost Mattermost affected 11.5.0 11.5.1 semver Not specified
CNA Mattermost Mattermost affected 10.11.0 10.11.13 semver Not specified
CNA Mattermost Mattermost unaffected 11.6.0 Not specified
CNA Mattermost Mattermost unaffected 11.5.2 Not specified
CNA Mattermost Mattermost unaffected 10.11.14 Not specified

References

ReferenceSourceLinkTags
mattermost.com/security-updates [email protected] mattermost.com Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: shoodagiri (en)

Additional Advisory Data

Solutions

CNA: Update Mattermost to versions 11.6.0, 11.5.2, 10.11.14 or higher.

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