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Response snapshot Oct 27, 2026, 07:22 UTC

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VulnerabilityCVE-2026-110725

fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references

`fast-uri`'s `serialize()`, `normalize()`, and `resolve()`, when called with the non-default option `reference: 'suffix'` on a reference that has no authority, emit a relative reference whose first path segment contains a bare colon without escaping it. RFC 3986 section 3.

Published Updated

At a glance

Exploited
Not known
Severity
3.7 Low (CVSS 3.1)
Chance of exploitation
0.3% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: fast-uri: 2.4.8; fast-uri: 3.1.9; fast-uri: 4.2.3. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-333x-w4r6-6crp (opens a new tab)

What happened

### Impact

`fast-uri`'s `serialize()`, `normalize()`, and `resolve()`, when called with the non-default option `reference: 'suffix'` on a reference that has no authority, emit a relative reference whose first path segment contains a bare colon without escaping it. RFC 3986 section 3.

3 requires the first segment of a `path-noscheme` reference not to contain a colon, precisely because a bare colon makes the string reparse as an absolute URI with a scheme. `fast-uri`'s default serialization escapes that colon, but the suffix path does not.

For example, `normalize('javascript:alert(1)', { reference: 'suffix' })` returns `javascript:alert(1)`, which reparses as a live `javascript:` scheme; `data:` and `vbscript:` behave the same.

Continue reading

Applications that serialize or normalize a relative reference with `reference: 'suffix'` and then treat the result as a URI can turn inert input into a live `javascript:`, `data:`, or `vbscript:` URL (a cross-site scripting vector), and `equal()` can conflate a scheme-bearing reference with a relative one. Exposure is limited to applications that use the non-default `reference: 'suffix'` option.

### Patches

Upgrade to `fast-uri` `2.4.8`, `3.1.9`, or `4.2.3`.

### Workarounds

Do not use the `reference: 'suffix'` option on untrusted input. If suffix output is required, percent-encode a colon in the first path segment of the result before treating it as a URI.

Affected package ranges reported by GitHub: fast-uri: < 2.4.8 fast-uri: >= 3.0.0, < 3.1.9 fast-uri: >= 4.0.0, < 4.2.3

Scores and how they were measured

CVSS base severity

3.7

Version 3.1As of

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.3%

Scored Percentile 22.8%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-333x-w4r6-6crp (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-333x-w4r6-6crp, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-110725, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 23). fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references (CVE-2026-110725). https://kevwire.com/record/CVE-2026-110725

MLA

"fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references (CVE-2026-110725)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-110725.

Chicago

KEVWire. "fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references (CVE-2026-110725)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-110725.

Evidence summary (plain text)

fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references (Oct 23, 2026).
`fast-uri`'s `serialize()`, `normalize()`, and `resolve()`, when called with the non-default option `reference: 'suffix'` on a reference that has no authority, emit a relative reference whose first path segment contains a bare colon without escaping it. RFC 3986 section 3.3 requires the first segment of a `path-noscheme` reference not to contain a colon, precisely because a bare colon makes the string reparse as an absolute URI with a scheme. `fast-uri`'s default serialization escapes that colon, but the suffix path does not.

For example, `normalize('javascript:alert(1)', { reference: 'suffix' })` returns `javascript:alert(1)`, which reparses as a live `javascript:` scheme; `data:` and `vbscript:` behave the same.
CVSS 3.7 (version 3.1; evidence as of Oct 23, 2026; https://github.com/advisories/GHSA-333x-w4r6-6crp).
EPSS 0.3% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-110725&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-333x-w4r6-6crp: https://github.com/advisories/GHSA-333x-w4r6-6crp
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-110725&date=2026-10-26
Record ID: CVE-2026-110725.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

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