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percent-encoded path separator in URL host

Project curl Security Advisory, May 11 2022 - Permalink


The curl URL parser wrongly accepts percent-encoded URL separators like '/' when decoding the hostname part of a URL, making it a different URL using the wrong hostname when it is later retrieved.

For example, a URL like, would be allowed by the parser and get transposed into This flaw can be used to circumvent filters, checks and more.


This flaw was introduced in commit 9a8564a920188e, shipped in curl 7.80.0 when curl added support for percent-encoded hostnames in URLs.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2022-27780 to this issue.

CWE-177: Improper Handling of URL Encoding

Severity: Medium


libcurl is used by many applications, but not always advertised as such!


The URL parser now rejects hostnames that percent-decode into URL separator characters.


A - Upgrade curl to version 7.83.1

B - Apply the patch to your local version


This issue was reported to the curl project on April 28, 2022. We contacted distros@openwall on May 5.

libcurl 7.83.1 was released on May 11 2022, coordinated with the publication of this advisory.


Thanks a lot!