fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding
CVSS score
6.1
EPSS probability
—
Risk score
0.6
Published
4 h ago
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Vulnerability description
CVE AI research
DayBreach AI Explanation
Verified against sourcesSources read
2
Source agreement
Tam uyum
Evidence confidence
%63
Short explanation
A vulnerability exists in the fast-uri library where the URI scheme component is percent-decoded before validation if it contains encoded characters. This issue can cause dangerous schemes to be emitted as live URLs and lead to cross-site scripting vectors.
This vulnerability allows attackers to bypass security filters and equality-based allowlists in applications, potentially resulting in stored or reflected cross-site scripting vectors.
What should be done?
- Upgrade fast-uri to versions 2.4.8, 3.1.9, 4.2.3, or later.
- Reject inputs whose scheme part contains a percent sign.
- Check the parsed scheme against an allowlist after normalization.
Chain of evidence and sources
fast-uri kütüphanesi, 2.4.8 öncesi, 3.0.0 ile 3.1.8 arası ve 4.0.0 ile 4.2.2 arasındaki sürümlerde şema bileşenini doğrulamadan önce unescape() ile yüzde kodunu çözmektedir.
Bu güvenlik açığı, siteler arası betik çalıştırma vektörlerine ve eşitliğe dayalı izin listelerinin baypas edilmesine neden olabilir.
Show the technical text from the sources
fast-uri is a dependency-free RFC 3986 URI parser and serializer for Node.js. In versions before 2.4.8, from 3.0.0 through 3.1.8, and from 4.0.0 through 4.2.2, fast-uri percent-decodes the scheme component with the legacy global unescape() function before validating it, so an input whose decoded scheme is a dangerous token is emitted as a live scheme even though RFC 3986 does not allow percent-encoding in a scheme and no other parser accepts it. An application that screens dangerous schemes on the raw input and then stores or renders the normalized or resolved result can turn an inert string into an executable javascript, data, or vbscript URL, producing a stored or reflected cross-site scripting vector, and the equal() comparison treats an encoded and a plain scheme as the same, which can bypass equality-based allowlists. The issue is fixed in fast-uri 2.4.8, 3.1.9, and 4.2.3, and users should upgrade to one of these versions or later. As a workaround, reject input whose scheme part contains a percent sign, or check the parsed scheme against an allowlist after normalization and use that same parsed result rather than the raw string.
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CWE: CWE-172, CWE-180
Explanation produced with the local gemini-flash-lite-latest model. Numerical metrics and the KEV, patch and exploit statuses are not determined by AI.
IMPACT: Affected Products and Software
Affected Products
The following products are affected by CVE-2026-110306 vulnerability. Where our threat engine knows the exact affected versions, they are listed below.
| ID | VENDOR | PRODUCT | ACTION |
|---|---|---|---|
| 1 | fast-uri | fast-uri | View |
RED HAT CSAF/VEX: Product Impact Check
SCORING: CVSS from Multiple Sources
CVSS Scores
The Common Vulnerability Scoring System is a standardised framework for assessing the severity of vulnerabilities in software and systems. We collect and display CVSS scores from several sources for each CVE.
| SCORE | VERSION | SEVERITY | VECTOR | SOURCE |
|---|---|---|---|---|
| 6.1 | CVSS V3_1 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N | CVE CNA |
| 6.1 | CVSS V31 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N | NVD |
Patch and Remediation Guide
Solution & Remediation Advisory
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Public exploit and active exploitation status
Verified exploit intelligence
No verified public PoC, exploit repository or Metasploit module has been found for this CVE yet.
Weakness Classification and Attack Patterns (CWE & CAPEC)
CWE - Common Weakness Enumeration
While CVE identifies specific instances of vulnerabilities, CWE categorises the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-110306 is associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-110306 weaknesses.
Attack Vector and Accessibility
Official Sources and Advisories
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