CVE-2026-16221

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 87% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this week
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 7.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
7.5
EG Score
7.5(medium)
EPSS
12.8%
KEV
Not listed

Published

July 19, 2026

Last Modified

July 21, 2026

Advisory Details (2)

Auto-updated Jul 19, 2026
Patch available. Sources: github.
github Patch Available

fast-uri vulnerable to host confusion via literal backslash authority delimiter · Advisory · fastify/fast-uri · GitHub

https://github.com/fastify/fast-uri/security/advisories/GHSA-v2hh-gcrm-f6hx
generic

Security Advisories | OpenJS Foundation CVE Numbering Authority

https://cna.openjsf.org/security-advisories.html

Vendor Advisories for CVE-2026-16221(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 7× in last 7d / 7× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 14:08 UTCEPSS rescore
  2. 2026-07-21 15:24 UTCEPSS rescore
  3. 2026-07-20 17:39 UTCEG score recompute
  4. 2026-07-20 17:08 UTCEPSS rescore
  5. 2026-07-19 15:58 UTCEG score recompute
  6. 2026-07-19 14:34 UTCEG score recompute
  7. 2026-07-19 14:34 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-16221?
CVE-2026-16221 is a high vulnerability published on July 19, 2026. 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…
When was CVE-2026-16221 disclosed?
CVE-2026-16221 was first published in the National Vulnerability Database on July 19, 2026, with the most recent update on July 21, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-16221 actively exploited?
CVE-2026-16221 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 12.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-16221?
CVE-2026-16221 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-16221?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-16221, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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