curl / Docs / Security Problems / percent-encoded path separator in URL host

percent-encoded path separator in URL host

Project curl Security Advisory, May 11 2022 - Permalink

VULNERABILITY

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

For example, a URL like http://example.com%2F10.0.0.1/, would be allowed by the parser and get transposed into http://example.com/10.0.0.1/. This flaw can be used to circumvent filters, checks and more.

We are not aware of any exploit of this flaw.

INFO

This flaw was introduced in commit 9a8564a920188e, shipped in curl 7.80.0 when curl added support for percent-encoded host names 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

AFFECTED VERSIONS

Affected versions: curl 7.80.0 to and including 7.83.0
Not affected versions: curl < 7.83.0 and curl >= 7.83.1

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

THE SOLUTION

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

A fix for CVE-2022-27780

RECOMMENDATIONS

A - Upgrade curl to version 7.83.1

B - Apply the patch to your local version

TIMELINE

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.

CREDITS

Reported-by: Axel Chong
Patched-by: Daniel Stenberg

Thanks a lot!