curl / Docs / Security Problems / URL Buffer Overflow

URL Buffer Overflow Vulnerability

Project curl Security Advisory, December 7th 2005 permalink


libcurl's URL parser function can overflow a malloced buffer in two ways, if given a too long URL.

These overflows happen if you

1 - pass in a URL with no protocol (like "http://") prefix, using no slash and the string is 256 bytes or longer. This leads to a single zero byte overflow of the malloced buffer.

2 - pass in a URL with only a question mark as separator (no slash) between the host and the query part of the URL. This leads to a single zero byte overflow of the malloced buffer.

Both overflows can be made with the same input string, leading to two single zero byte overwrites.

The affected flaw cannot be triggered by a redirect, but the long URL must be passed in "directly" to libcurl. It makes this a "local" problem. Of course, lots of programs may still pass in user-provided URLs to libcurl without doing much syntax checking of their own, allowing a user to exploit this vulnerability.

There is no known exploit at the time of this writing.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2005-4077 to this issue.

CWE-122: Heap-based Buffer Overflow


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


We suggest you take one of the following actions immediately:

A - Upgrade to curl and libcurl 7.15.1

B - Apply the patch to your libcurl version and install this

C - Make sure the URLs you pass to libcurl always have a protocol part prepended


We were notified by Stefan Esser on November 29th, 2005.

Discussions were held and the patch to fix this flaw was made swiftly.

Dec 12 2005: Additional info on what's required for 7.14.0 and earlier was provided by Wilfried Weissmann in a Redhat bug report. The provided patch above was updated and adjusted to the newly discovered facts.


Thanks a lot!