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local file overwrite

Project curl Security Advisory, October 13th 2010 Permalink


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 Symbian.

This error is only present in the curl command line tool, it is NOT a problem of the library libcurl.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2010-3842 to this issue.

CWE-30: Path Traversal

Severity: High


Also note that curl is used by many applications, and not always advertised as such.


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 preference:

A - Upgrade to curl and libcurl 7.21.2

B - Apply patch and rebuild

C - Stop using the --remote-header-name/-J option


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 4th.

curl 7.21.2 was released on October 13th 2010, just before this flaw was publicly disclosed.


Thanks a lot!