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invalid URL parsing with '#'

Project curl Security Advisory, November 2, 2016 - Permalink

VULNERABILITY

curl doesn't parse the authority component of the URL correctly when the host name part ends with a '#' character, and could instead be tricked into connecting to a different host. This may have security implications if you for example use a URL parser that follows the RFC to check for allowed domains before using curl to request them.

Passing in http://example.com#@evil.com/x.txt would wrongly make curl send a request to evil.com while your browser would connect to example.com given the same URL.

The problem exists for most protocol schemes.

We are not aware of any exploit of this flaw.

INFO

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2016-8624 to this issue.

AFFECTED VERSIONS

This flaw exists in the following curl versions.

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

THE SOLUTION

In version 7.51.0, the parser function is fixed.

A patch for CVE-2016-8624 is available.

As a side-effect of this fix, using the # character as part of the user or password fields in the URL is no longer supported. According to RFC 3986 section 2.3 it isn't allowed. See issue #1216

RECOMMENDATIONS

We suggest you take one of the following actions immediately, in order of preference:

A - Upgrade curl and libcurl to version 7.51.0

B - Apply the patch to your version and rebuild

C - Strip out the parts of the URLs containing '#' before passing them to curl

TIME LINE

It was first reported to the curl project on October 10 by Fernando Muñoz.

We contacted distros@openwall on October 19.

curl 7.51.0 was released on November 2 2016, coordinated with the publication of this advisory.

CREDITS

Thanks to Fernando Muñoz!