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curl / Docs / Security Problems / wrong re-use of connections

wrong re-use of connections

Project curl Security Advisory, March 26th 2014 permalink


libcurl can in some circumstances re-use the wrong connection when asked to do transfers using other protocols than HTTP and FTP.

libcurl features a pool of recent connections so that subsequent requests can re-use an existing connection to avoid overhead.

When re-using a connection a range of criterion must first be met. Due to an error in the code, a transfer that was initiated by an application could wrongfully re-use an existing connection to the same server that was authenticated using different credentials. The existing logic basically only worked well enough for HTTP and FTP, while all other network protocols were silently, but erroneously, assumed to work like HTTP. Basically, protocols that use connection oriented authentication need a new connection when new credentials are used.

Affected protocols include: SCP, SFTP, POP3(S), IMAP(S), SMTP(S) and LDAP(S).

Applications can disable libcurl's re-use of connections and thus mitigate this problem, by using one of the following libcurl options to alter how connections are or aren't re-used: CURLOPT_FRESH_CONNECT, CURLOPT_MAXCONNECTS and CURLMOPT_MAX_HOST_CONNECTIONS (if using the curl_multi API).

(This problem is very similar to a problem previously reported to NTLM HTTP connections, named CVE-2014-0015)

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2014-0138 to this issue.

CWE-305: Authentication Bypass by Primary Weakness


This flaw has existed ever since libcurl started to support these other protocols, although the code has been restructured a few times over the years so the mistake has altered shape.

libcurl is used by many applications, but not always advertised as such!


libcurl 7.36.0 makes sure that connections are re-used more strictly.

A patch for this problem is available


We suggest you take one of the following actions immediately, in order of preference:

A - Upgrade to curl and libcurl 7.36.0

B - Apply the patch and rebuild libcurl


It was reported to the curl project on February 15th 2014. We contacted distros@openwall on March 16 2014.

libcurl 7.36.0 was released on March 26th 2014, coordinated with the publication of this advisory.


Bug reported and patch written by Steve Holme.

Thanks a lot!