[SECURITY ADVISORY] curl: percent-encoded path separator in URL host

[Daniel Stenberg <daniel () haxx se>]

percent-encoded path separator in URL host
==========================================

Project curl Security Advisory, May 11 2022 -
[Permalink](https://curl.se/docs/CVE-2022-27780.html)

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](https://github.com/curl/curl/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](https://github.com/curl/curl/commit/914aaab9153764e)

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
-------

This issue was reported by Axel Chong. Patched by Daniel Stenberg.

Thanks a lot!

--

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