Open redirect via incomplete pathname sanitization
Published Apr 17, 2026 · Updated Apr 17, 2026
Open redirect in next-intl before 4.9.1 allows remote attackers to send browsers off-site through crafted localized paths. The middleware's sanitizePathname function failed to remove tab, line-feed, and carriage-return characters before the WHATWG URL parser could collapse a relative path into a scheme-relative external URL. Exposure requires the middleware with localePrefix set to as-needed; the direct result is navigation to an attacker-chosen host from a trusted application URL.
Summary
What happened
Open redirect in next-intl before 4.9.1 allows remote attackers to send browsers off-site through crafted localized paths. The middleware's sanitizePathname function failed to remove tab, line-feed, and carriage-return characters before the WHATWG URL parser could collapse a relative path into a scheme-relative external URL. Exposure requires the middleware with localePrefix set to as-needed; the direct result is navigation to an attacker-chosen host from a trusted application URL.
The record
- CVE
- CVE-2026-40299
- Published
- Apr 17, 2026
- Updated
- Apr 17, 2026
- Vendor
- Jan Amann
- Product
- next-intl
- Classifications
- CWE-601, T1566.002
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 17, 2026CVE publishedPublication date reported by the CVE source.
- Apr 17, 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.
- Affected versionversion=< 4.9.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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