Medium 4.1Published Aug 21, 2026

CVE-2026-63466Unleash: Global Mustache.escape override disables HTML escaping process-wide, enabling Slack/Teams link-injection via unrestricted username

Updated under an hour ago (2026-10-19 08:30 UTC)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

Unleash 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.

CVSS: 4.1 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N
Weakness (CWE): CWE-116
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Aug 21, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Unleash unleash unleash:unleash (from the name)	before 8.0.3	CNA record

References

https://github.com/Unleash/unleash/security/advisories/GHSA-w4mq-xh27-6xpxx-refsource-confirm
https://github.com/Unleash/unleash/commit/002012cfdbedd2e9b7db9dc83b9f549f761db22ex-refsource-misc
https://github.com/Unleash/unleash/releases/tag/v8.0.3x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.