Encoding Error 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-19846651
- published16 Sept 2026
- disclosed15 Sept 2026
- creditmanus-use, 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 Encoding Error in the mailto parser process. An attacker can inject unauthorized recipients or manipulate the subject and body fields by crafting a URI with percent-encoded reserved field names, which are not properly recognized during parsing but are re-emitted as literal field names upon serialization. This can result in attacker-controlled data being silently included in outgoing messages or logs.
Workaround
This vulnerability can be mitigated by decoding and re-validating the recipient, subject, and body fields of a mailto URI after serialization and before acting on it.