CVE-2026-75975Public exploitNetwork attack vector

SSRF via malformed IPv6 normalization

Published Aug 24, 2026 · Updated Aug 24, 2026

SSRF in fast-uri 2.3.1 through 2.4.4, 3.0.0 through 3.1.5, and 4.0.0 through 4.1.2 allows remote attackers to reach private IPv6 hosts. The bracketed-IPv6 parser truncates invalid trailing text, normalizes the malformed host into a different valid address, and leaves the parse error unset. Exploitation requires an application to normalize attacker-controlled URLs before requesting, redirecting, routing, or enforcing host policy, enabling access to loopback, unique-local, or link-local destinations.

CVSS severity7.5
High
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in fast-uri 2.3.1 through 2.4.4, 3.0.0 through 3.1.5, and 4.0.0 through 4.1.2 allows remote attackers to reach private IPv6 hosts. The bracketed-IPv6 parser truncates invalid trailing text, normalizes the malformed host into a different valid address, and leaves the parse error unset. Exploitation requires an application to normalize attacker-controlled URLs before requesting, redirecting, routing, or enforcing host policy, enabling access to loopback, unique-local, or link-local destinations.

The record

CVE
CVE-2026-75975
Published
Aug 24, 2026
Updated
Aug 24, 2026
Vendor
Fastify
Product
fast-uri
Classifications
CWE-918, CWE-20, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 24, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.3.1 <2.4.5
  2. Affected versionversion=3.0.0 <3.1.6
  3. Affected versionversion=4.0.0 <4.1.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fastify · fast-uriversion=2.3.1 <2.4.5; version=3.0.0 <3.1.6; version=4.0.0 <4.1.3

Published CVSS scores

7.5OpenJS FoundationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
CWE-20Improper Input Validation
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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