Path-policy bypass via premature percent-decoding
Published May 4, 2026 · Updated May 4, 2026
Path traversal in Fastify fast-uri before 3.1.1 allows remote attackers to bypass path-based policy via crafted URLs. The normalize() and equal() functions decode percent-encoded separators and dot segments before removing dot segments, turning encoded path data into live slashes and parent-directory references. Exploitation requires a consuming application to apply these functions to attacker-controlled URLs for path confinement or comparison, allowing an apparently permitted path to resolve outside the intended location.
Summary
What happened
Path traversal in Fastify fast-uri before 3.1.1 allows remote attackers to bypass path-based policy via crafted URLs. The normalize() and equal() functions decode percent-encoded separators and dot segments before removing dot segments, turning encoded path data into live slashes and parent-directory references. Exploitation requires a consuming application to apply these functions to attacker-controlled URLs for path confinement or comparison, allowing an apparently permitted path to resolve outside the intended location.
The record
- CVE
- CVE-2026-6321
- Published
- May 4, 2026
- Updated
- May 4, 2026
- Vendor
- Fastify
- Product
- fast-uri
- Classifications
- CWE-22
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 4, 2026CVE publishedPublication date reported by the CVE source.
- May 4, 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?
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- Affected versionversion=0 <3.1.1
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What is affected?
Published CVSS scores
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Attacks
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Technologies
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Your stack
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