Security Advisory March 3 2009
libcurl Arbitrary File Access
Project cURL Security Advisory, March 3rd 2009
When told to follow a "redirect" automatically, libcurl does not question
the new target URL but will follow to any new URL that it understands. As
libcurl supports FILE:// URLs, a rogue server can thus "trick" a
libcurl-using application to read a local file instead of the remote one.
This is a problem, for example, when the application is running on a server
and is written to upload or to otherwise provide the transfered data to a
user, to another server or to another application etc, as it can be used to
expose local files it was not meant to.
The problem can also be exploited for uploading, if the rogue server
redirects the client to a local file and thus it would (over)write a local
file instead of sending it to the server.
libcurl compiled to support SCP can get tricked to get a file using embedded
semicolons, which can lead to execution of commands on the given
server. "Location: scp://name:passwd@host/a'``;date >/tmp/test``;'".
Files on servers other than the one running libcurl are also accessible when
credentials for those servers are stored in the .netrc file of the user
running libcurl. This is most common for FTP servers, but can occur with
any protocol supported by libcurl. Files on remote SSH servers are also
accessible when the user has an unencrypted SSH key.
There is no known exploit at the time of this writing.
The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2009-0037 to this issue.
2. AFFECTED VERSIONS
Affected versions: curl and libcurl 5.11(!) to and including 7.19.3
Not affected versions: curl and libcurl 5.10 and earlier, 7.19.4 and later
Also note that (lib)curl is used by many applications, and not always
advertised as such.
3. THE SOLUTION
libcurl 7.19.4 introduces a new option called CURLOPT_REDIR_PROTOCOLS, which
applications can use to tell libcurl what target protocols automatic
redirect followings are allowed to use. This will by default exclude FILE
and SCP URLs.
We suggest you take one of the following actions immediately, in order of
A - Upgrade to curl and libcurl 7.19.4
B - Apply the suitable patch and rebuild
For current CVS HEAD:
For curl 7.19.0:
For curl 7.18.2:
For curl 7.18.1:
For curl 7.17.0:
For curl 7.16.4:
For curl 7.15.3:
For curl 7.15.1:
For curl 7.11.0:
C - Disable automatic redirection following in your application and do the
logic "manually" instead.
5. TIME LINE
We were notified by David Kierznowski on Feb 6th, 2009.
We discussed solutions and a first patch was written and tested on Feb 11th.
Vendor-sec was contacted on Feb 12, 2009.
We agreed on and coordinated the synchronous disclosure of this problem
together with the curl 7.19.4 release.
curl 7.19.4 was released on March 3 2009, just before this flaw was publicly
Reported to us by David Kierznowski. Thanks a lot!
Daniel Fandrich researched the issue and helped with the fix.
Michal Marek brought the SCP side of this issue and did a bunch of the
Daniel Stenberg wrote the primary patch and this advisory.