Hostname validation bypass via backslash scheme delimiter
Published Feb 21, 2021 · Updated Aug 3, 2024
URL parsing in URI.js before 1.19.6 allows attackers to spoof a hostname with a backslash in the scheme delimiter. URI.parse() recognizes only two forward slashes after a scheme, so a mixed slash-backslash delimiter is treated as a relative path and returns no hostname. Applications are exposed when attacker-controlled URLs drive hostname-based security decisions, enabling allowlist bypass, SSRF, or open redirects.
Summary
What happened
URL parsing in URI.js before 1.19.6 allows attackers to spoof a hostname with a backslash in the scheme delimiter. URI.parse() recognizes only two forward slashes after a scheme, so a mixed slash-backslash delimiter is treated as a relative path and returns no hostname. Applications are exposed when attacker-controlled URLs drive hostname-based security decisions, enabling allowlist bypass, SSRF, or open redirects.
The record
- CVE
- CVE-2021-27516
- Published
- Feb 21, 2021
- Updated
- Aug 3, 2024
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-20
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 21, 2021CVE publishedPublication date reported by the CVE source.
- Aug 3, 2024Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What is affected?
Affected products and versions are unavailable in this record.
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
- Backslash scheme-delimiter hostname-spoofing exampleproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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