Unleash: Global Mustache.escape override disables HTML escaping process-wide, enabling Slack/Teams link-injection via unrestricted username

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63466
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-21 19:17:32 UTC
Updated2026-08-21 22:16:42 UTC
DescriptionUnleash is an open-source feature management platform. Prior to 8.0.3, FeatureEventFormatterMd.format in src/lib/addons/feature-event-formatter-md.ts assigns Mustache.escape to an identity function before rendering action and path templates. Because Mustache.escape is process-wide, the assignment disables escaping for subsequent Mustache.render calls in email-service.ts, webhook.ts, datadog.ts, and new-relic.ts. An editor-level user can place Slack or Microsoft Teams link syntax in an unrestricted username, trigger a feature event, and inject an attacker-labeled link into a trusted outbound notification channel, while other Mustache sinks remain unescaped until restart. This issue is fixed in version 8.0.3.

Risk And Classification

Primary CVSS: v3.1 4.1 MEDIUM from [email protected]

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

Problem Types: CWE-116 | CWE-116 CWE-116: Improper Encoding or Escaping of Output

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.1MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N
3.1CNADECLARED4.1MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Unleash Unleash affected < 8.0.3 Not specified

References

ReferenceSourceLinkTags
github.com/Unleash/unleash/commit/002012cfdbedd2e9b7db9dc83b9f549f761db22e [email protected] github.com
github.com/Unleash/unleash/releases/tag/v8.0.3 [email protected] github.com
github.com/Unleash/unleash/security/advisories/GHSA-w4mq-xh27-6xpx [email protected] github.com
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