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Response snapshot Oct 27, 2026, 04:01 UTC

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VulnerabilityCVE-2026-110180

fast-uri vulnerable to host confusion via unchecked WHATWG host canonicalization

`fast-uri` versions `>= 2.4.2, = 3.1.3, = 4.0.1, <= 4.2.2` can silently rewrite the host of an HTTP-family URL (`http`, `https`, `ws`, `wss`, or any scheme with `domainHost: true`). For those schemes `canonicalizeHost()` passes the parsed host to the WHATWG `URL` parser and adopts its `.

Published Updated

At a glance

Exploited
Not known
Severity
4.8 Medium (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-wjr9-j795-jxcr (opens a new tab)

What happened

### Impact

`fast-uri` versions `>= 2.4.2, = 3.1.3, = 4.0.1, <= 4.2.2` can silently rewrite the host of an HTTP-family URL (`http`, `https`, `ws`, `wss`, or any scheme with `domainHost: true`). For those schemes `canonicalizeHost()` passes the parsed host to the WHATWG `URL` parser and adopts its `.hostname` without checking that the parser read the whole input as a host.

RFC 3986 permits `@` inside the host group and the WHATWG parser strips TAB, LF, and CR, so the authority `fast-uri` reports is rewritten by that second parser with no `error` set: data before an `@` is dropped and whitespace is removed.

For example, `fast-uri` parses `http://a@b@evil.example/` to host `evil.example` (dropping the `b` segment), and a host containing a raw TAB, CR, or LF has those characters stripped. `equal()` then treats a whitespace-smuggled host as the same as the clean one, and `resolve()` rewrites the authority the same way.

Continue reading

Applications that use `fast-uri` to enforce host-based policy (denylists, loopback filtering, redirect validation, outbound proxy routing) on one representation, such as the raw input, see a policy/use desync: the canonical host `fast-uri` returns differs from what was checked, and traffic can be steered to an unintended destination.

### Patches

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

### Workarounds

Reject URIs whose authority contains more than one `@`, or contains TAB, CR, or LF, before calling `fast-uri`. Alternatively, treat any non-empty `parse(x).error` as fatal, and compare hosts only from the same `parse()` result.

Affected package ranges reported by GitHub: fast-uri: >= 2.4.2, < 2.4.8 fast-uri: >= 3.1.3, < 3.1.9 fast-uri: >= 4.0.1, < 4.2.3

Scores and how they were measured

CVSS base severity

4.8

Version 3.1As of

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/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 16.9%

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-wjr9-j795-jxcr (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-wjr9-j795-jxcr, 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-2026-110180, 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 host confusion via unchecked WHATWG host canonicalization (CVE-2026-110180). https://kevwire.com/record/CVE-2026-110180

MLA

"fast-uri vulnerable to host confusion via unchecked WHATWG host canonicalization (CVE-2026-110180)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-110180.

Chicago

KEVWire. "fast-uri vulnerable to host confusion via unchecked WHATWG host canonicalization (CVE-2026-110180)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-110180.

Evidence summary (plain text)

fast-uri vulnerable to host confusion via unchecked WHATWG host canonicalization (Oct 23, 2026).
`fast-uri` versions `>= 2.4.2, = 3.1.3, = 4.0.1, <= 4.2.2` can silently rewrite the host of an HTTP-family URL (`http`, `https`, `ws`, `wss`, or any scheme with `domainHost: true`). For those schemes `canonicalizeHost()` passes the parsed host to the WHATWG `URL` parser and adopts its `.hostname` without checking that the parser read the whole input as a host. RFC 3986 permits `@` inside the host group and the WHATWG parser strips TAB, LF, and CR, so the authority `fast-uri` reports is rewritten by that second parser with no `error` set: data before an `@` is dropped and whitespace is removed.

For example, `fast-uri` parses `http://a@b@evil.example/` to host `evil.example` (dropping the `b` segment), and a host containing a raw TAB, CR, or LF has those characters stripped. `equal()` then treats a whitespace-smuggled host as the same as the clean one, and `resolve()` rewrites the authority the same way.
CVSS 4.8 (version 3.1; evidence as of Oct 23, 2026; https://github.com/advisories/GHSA-wjr9-j795-jxcr).
EPSS 0.3% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-110180&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-wjr9-j795-jxcr: https://github.com/advisories/GHSA-wjr9-j795-jxcr
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-2026-110180&date=2026-10-26
Record ID: CVE-2026-110180.
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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