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[SECURITY ADVISORY] lingering HTTP credentials in connection re-use

From: Daniel Stenberg <>
Date: Wed, 17 Jun 2015 08:11:54 +0200 (CEST)

lingering HTTP credentials in connection re-use

Project cURL Security Advisory, June 17th 2015 -


libcurl can wrongly send HTTP credentials when re-using connections.

libcurl allows applications to set credentials for the upcoming transfer with
HTTP Basic authentication, like with `CURLOPT_USERPWD` for example. Name and
password. Just like all other libcurl options the credentials are sticky and
are kept associated with the "handle" until something is made to change the

Further, libcurl offers a `curl_easy_reset()` function that resets a handle
back to its pristine state in terms of all settable options. A reset is of
course also supposed to clear the credentials. A reset is typically used to
clear up the handle and prepare it for a new, possibly unrelated, transfer.

Within such a handle, libcurl can also store a set of previous connections in
case a second transfer is requested to a host name for which an existing
connection is already kept alive.

With this flaw present, using the handle even after a reset would make libcurl
accidentally use those credentials in a subseqent request if done to the same
host name and connection as was previously accessed.

An example case would be first requesting a password protected resource from
one section of a web site, and then do a second request of a public resource
from a completely different part of the site without authentication. This flaw
would then inadvertently leak the credentials in the second request.

We are not aware of any exploit of this flaw.


This flaw can also affect the curl command line tool if a similar operation
series is made with that.
The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2015-3236 to this issue.
This flaw is relevant for
- Affected versions: libcurl 7.40.0 to and including 7.42.1
- Not affected versions: libcurl < 7.40.0 and libcurl >= 7.43.0
libcurl is used by many applications, but not always advertised as such!
In version 7.43.0, libcurl properly clears the credentials and prevents them
from lingering around.
A patch for this problem that changes the default is available at (URL will be
updated in final advisory):
We suggest you take one of the following actions immediately, in order of
  A - Upgrade curl and libcurl to version 7.43.0
  B - Apply the patch to your version and rebuild
  C - If you use `curl_easy_reset()`, explicitly set the credentials afterwards
It was first reported to the curl project on May 19 2015. We contacted
distros_at_openwall on June 11.
libcurl 7.43.0 was released on June 17 2015, coordinated with the publication
of this advisory.
Reported by Tomas Tomecek and Kamil Dudka.
Thanks a lot!
List admin:
Received on 2015-06-17