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CVE-2026-76172

HIGHCVSS 7.5/10EPSS 0.25%

Last modified

CVE-2026-76172 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. EPSS estimates a 0.25% chance of exploitation in the next 30 days.

Description

fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. As a result an input whose scheme carries percent-encoded slashes parses as a scheme with no authority, so the parsed host and error are both undefined, yet resolving or normalizing that same input emits a network-path reference whose authority is attacker-chosen and re-parses to that host. An application that allowlists on the parsed host, or treats a reference with no authority as safe to resolve against its base, gets the opposite of what it checked, giving an off-site redirect, server-side request forgery, or address-policy bypass. The legacy decoder also expands non-standard escape forms, widening the issue past upstream filters, and control characters in the scheme can reach the output as raw carriage return and line feed. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 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 reject a scheme that is not valid after decoding. Users should upgrade to a patched version.

Metrics

CVSS 3.1
7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability
0.25%

15.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
OpenjsfFast-Uri>= 2.3.1, < 2.4.5
OpenjsfFast-Uri>= 3.0.0, < 3.1.6
OpenjsfFast-Uri>= 4.0.0, < 4.1.3

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-76172?
fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. As a result an input whose scheme carries percent-encoded slashes parses as a scheme with no authority, so the parsed host and error are both undefined, yet resolving or normalizing that same input emits a network-path reference whose authority is attacker-chosen and re-parses to that host. An application that allowlists on the parsed host, or treats a reference with no authority as safe to resolve against its base, gets the opposite of what it checked, giving an off-site redirect, server-side request forgery, or address-policy bypass. The legacy decoder also expands non-standard escape forms, widening the issue past upstream filters, and control characters in the scheme can reach the output as raw carriage return and line feed. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 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 reject a scheme that is not valid after decoding. Users should upgrade to a patched version.
How severe is CVE-2026-76172?
CVE-2026-76172 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.25% probability of exploitation in the next 30 days.
How do I fix CVE-2026-76172?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST