High severity · published Aug 24, 2026
CVE-2026-75899
fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding
7.5
CVSS
0.2%
EPSS
No
On KEV
Description
fast-uri is a URI parser for Node.js. It decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition, so a single call to normalize or resolve can turn nested percent-encoded input into a different network destination such as a loopback hostname or address. For example, a doubly encoded host that spells out a loopback name decodes to that live host in one operation, which contradicts RFC 3986 section 2.4 that an implementation must not decode the same string more than once. An application that normalizes or resolves an untrusted HTTP-family URI before outbound routing, redirect validation, or a host-policy check can receive a destination different from the one the original encoded host represented, giving a server-side request forgery and host-policy bypass primitive. This is an incomplete-fix variant of CVE-2026-6322. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which normalize percent escapes once and preserve encoded percent signs. Users should upgrade to a patched version.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 12% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FA
fast-uri · fast-uri
2.4.1 before 2.4.5; 3.1.2 before 3.1.6; 4.0.0 before 4.1.3 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-75899
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-75899
Vendor Advisory
https://cna.openjsf.org/security-advisories.html
Mitigation
https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf
More from fast-uri
7.5
CVE-2026-84394
fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority
7.5
CVE-2026-84292
fast-uri vulnerable to authority injection via an unvalidated port in serialize
7.5
CVE-2026-76172
fast-uri vulnerable to host confusion via percent-encoded scheme normalization
7.5
CVE-2026-75975
fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization
7.5
CVE-2026-75931
fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
