7.5

CVE-2026-16221: fast-uri vulnerable to host confusion via literal backslash authority delimiter

Analyzed
AliasesUBUNTU-CVE-2026-16221DEBIAN-CVE-2026-16221CGA-2hpm-fprq-jjf4
Published 19-07-2026Last modified 20-07-2026

Vulnerability summary

CVE-2026-16221 is a high (CVSS 7.5) Interpretation Conflict vulnerability in fast-uri. EPSS estimates a 0.44% chance of exploitation in the next 30 days, higher than 37.8% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 7.5 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
7.5/10
010
High · v3.1 (CVE.org)
EPSS score
0.44%
0%100%
Low · +0.18 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 2 · Related 1
RHSA-2026:54517RHSA-2026:54518CGA-V6H3-F8JX-F899

Timeline

  1. 19-07-2026
    PublishedVulnerability first disclosed.
  2. 20-07-2026
    Last modifiedVulnerability information updated.

Description

Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node's native WHATWG URL parser, used by fetch, undici, and Node's http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node's URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. Patches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3. Workarounds: none.

CVSS metrics

7 scores · 7 sources · 1 version

EPSS trend

Probability

0.44%

Chance of exploitation in the next 30 days

Percentile

38%

Versus all other CVEs

30-day change

Increase +0.18 pp

From 0.25% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Chainguard114 products
  • airflow-2All versions (No fix recorded)
  • airflow-core-2All versions (No fix recorded)
  • arangodb-3.12< 3.12.9.4-r15
  • argo-workflows-ui-3.7< 3.7.17-r0
  • argo-workflows-ui-4.0< 4.0.8-r0 | < 4.0.11-r0
Wolfi25 products
  • argo-workflows-ui-3.7< 3.7.17-r0
  • argo-workflows-ui-4.0< 4.0.8-r0 | < 4.0.11-r0
  • jupyter-base-notebook< 7.6.3-r2
  • langfuse-3< 3.224.1-r0
  • langfuse-3-compat< 3.225.7-r6
Debian1 product
  • node-ajvAll versions (No fix recorded) | < 8.20.0~ds+~cs7.1.2-1
Fast-uri1 product
  • fast-uri≥ 2.3.1, < 2.4.3 | ≥ 3.0.0, < 3.1.4 | ≥ 4.0.0, < 4.1.1
Npm1 product
  • fast-uri≥ 2.3.1, < 2.4.3 | ≥ 3.0.0, < 3.1.4 | ≥ 4.0.0, < 4.1.1
Openjsf1 product
  • fast-uri≥ 2.3.1, < 2.4.3 | ≥ 3.0.0, < 3.1.4 | ≥ 4.0.0, < 4.1.1
Ubuntu1 product
  • node-ajvAll versions (No fix recorded)

7 vendors · 144 products

References

14 links
Show all 14 references