Inappropriate Encoding for Output Context Affecting fast-uri package, versions >=4.1.3 <4.1.5
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-FASTURI-19846653
- published16 Sept 2026
- disclosed15 Sept 2026
- creditJace, manus-pi
Introduced: 15 Sep 2026
NewCVE-2026-86818 (opens in a new tab)How to fix?
Upgrade fast-uri to version 4.1.5 or higher.
Overview
fast-uri is a Dependency-free RFC 3986 URI toolbox
Affected versions of this package are vulnerable to Inappropriate Encoding for Output Context in the mailto parser when handling percent-encoded query field names. An attacker can manipulate email recipients, subjects, or body content by crafting specially formatted mailto URIs that exploit the desynchronization between parsing and serialization. This may result in emails being sent to unintended recipients or with altered content.