CVE-2026-63466 json
Unleash: Global Mustache.escape override disables HTML escaping process-wide, enabling Slack/Teams link-injection via unrestricted username
published 2mo ago modified 28d ago also GHSA-w4mq-xh27-6xpx , EUVD-2026-64042
- cvss
- 4.1
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.3%
- EPSS 0.3% chance of exploitation in 30 days, percentile 25%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- npm unleash-server 8.0.3
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Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 2mo ago
Exploit prediction
0.32% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 4.1 | CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N |
| GitHub | 3.1 | 4.1 | CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| npm | unleash-server | <8.0.3 |
8.0.3 |
Affected products
- Unleash unleash
Classification
- Weakness
-
- CWE-116 Improper Encoding or Escaping of Output
References
Sources
- CVE List CVE-2026-63466
- GitHub Advisory GHSA-w4mq-xh27-6xpx
- NVD CVE-2026-63466
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