Security Advisory October 13 2010
curl local file overwrite
Project curl Security Advisory, October 13th 2010
curl offers a command line option --remote-header-name (also usable as -J)
which will use the file name of the Content-disposition: header when it
saves the downloaded data locally.
curl attempts to cut off the directory parts from any given file name in the
header to only store files in the current directory. It will overwrite a
local file using the same name as the header specifies.
The stripping of the directory did not take backslashes into account. On
some operating systems, backslashes are used to separate directories and
file names. This allows a rogue server to send back a response that
overwrites a file name in the local machine that the user is allowed to
write, potentially a system file, a command or a known executable.
Operating systems affected include Windows, Netware, MSDOS, OS/2 and
This error is only present in the curl command line tool, it is NOT a
problem of the library libcurl.
There is no known exploit for this problem.
The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2010-3842 to this issue.
2. AFFECTED VERSIONS
Affected versions: curl 7.20.0 to and including 7.21.1
Not affected versions: curl < 7.20.0 and >= 7.21.2
Also note that curl is used by many applications, and not always advertised
3. THE SOLUTION
libcurl 7.21.2 makes sure that it will also strip off paths specified using
backslashes as path separator.
We suggest you take one of the following actions immediately, in order of
A - Upgrade to curl and libcurl 7.21.2
B - Apply this patch and rebuild
C - Stop using the --remote-header-name/-J option
5. TIME LINE
Dan Fandrich realized the problem exists and reported to the rest of the
team on September 3 2010.
We discussed solutions and a first patch was written and tested on September
curl 7.21.2 was released on October 13th 2010, just before this flaw was
Reported to us by Dan Fandrich. Thanks a lot!
Daniel Stenberg wrote the primary patch and this advisory