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VulnerabilityPublished

CVE-2026-110306: fast-uri · Encoding Error

Affects fast-uriSource CVE Database V5

0

Not known to be exploited · CVSS 6.1 Medium · fixed in 4.2.3 : update fast-uri when convenient.

Data as of 26 Oct 2026, 14:18 UTC

CVSS 3.1 base score
6.1Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 16% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-20.

Patch
Available – fixed in 4.2.3, 3.1.9, 2.4.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 20 Oct 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade fast-uri to 4.2.3, 3.1.9 or 2.4.8.

Affected software

ProductAffectedFixed in
fast-urifast-uriAffected
  • >=4.0.0 <4.2.3
Fixed in
  • 4.2.3
fast-urifast-uriAffected
  • >=3.0.0 <3.1.9
Fixed in
  • 3.1.9
fast-urifast-uriAffected
  • <2.4.8
Fixed in
  • 2.4.8
npmfast-uripkg:npm/fast-uriOther threatsAffected
  • <2.4.8
  • >=3.0.0 <3.1.9
  • >=4.0.0 <4.2.3
Fixed in
  • 2.4.8
  • 3.1.9
  • 4.2.3

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

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.

References

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