Date: Mon, 05 Sep 2016 14:14:32 +0200 From: Kamil Dudka <kdudka@...hat.com> To: curl-users@...l.haxx.se, curl-announce@...l.haxx.se, libcurl hacking <curl-library@...l.haxx.se>, oss-security@...ts.openwall.com Cc: Daniel Stenberg <daniel@...x.se> Subject: Re: [SECURITY VULNERABILITY] curl: Re-using connections with wrong client cert On Wednesday, August 03, 2016 09:05:26 Daniel Stenberg wrote: > Re-using connections with wrong client cert > =========================================== > > Project cURL Security Advisory, August 3rd 2016 - > [Permalink](https://curl.haxx.se/docs/adv_20160803B.html) After torture-testing the patch for CVE-2016-5420, it was discovered that libcurl built on top of NSS (Network Security Services) still incorrectly re-uses client certificates if a certificate from file is used for one TLS connection but no certificate is set for a subsequent TLS connection. This problem was caused by an implementation detail of the NSS backend in libcurl, which is orthogonal to the cause of CVE-2016-5420. Users of libcurl/NSS that load client certificates from files are encouraged to also apply the attached follow-up patch. The original patch for CVE-2016-5420 has been amended to also contain the attached patch: https://curl.haxx.se/CVE-2016-5420.patch > VULNERABILITY > ------------- > > libcurl did not consider client certificates when reusing TLS connections. > > libcurl supports reuse of established connections for subsequent requests. > It does this by keeping a few previous connections "alive" in a connection > pool so that a subsequent request that can use one of them instead of > creating a new connection will do so. > > When using a client certificate for a connection that was then put into the > connection pool, that connection could then wrongly get reused in a > subsequent request to that same server that either didn't use a client > certificate at all or that asked to use a different client certificate thus > trying to tell the user that it is a different entity. > > This mistakenly using the wrong connection could of course lead to > applications sending requests to the wrong realms of the server using > authentication that it wasn't supposed to have for those operations. > > We are not aware of any exploit of this flaw. > > INFO > ---- > > This flaw also affects the curl command line tool. > > The Common Vulnerabilities and Exposures (CVE) project has assigned the name > CVE-2016-5420 to this issue. > > AFFECTED VERSIONS > ----------------- > > This flaw is relevant for all versions of curl and libcurl that support > SSL/TLS and client certificates. > > - Affected versions: libcurl 7.1 to and including 7.50.0 > - Not affected versions: libcurl >= 7.50.1 > > libcurl is used by many applications, but not always advertised as such! > > THE SOLUTION > ------------ > > In version 7.50.1, curl will check that re-used connections have the correct > client certificate (file name) before used. > > A [patch for CVE-2016-5420](https://curl.haxx.se/CVE-2016-5420.patch) is > available. This patch relies on the > [CVE-2016-5419](https://curl.haxx.se/docs/adv_20160803A.html) patch already > having been applied. > > RECOMMENDATIONS > --------------- > > We suggest you take one of the following actions immediately, in order of > preference: > > A - Upgrade curl and libcurl to version 7.50.1 > > B - Apply the patch to your version and rebuild > > C - Do not use client certificates > > TIME LINE > --------- > > This was figured out by curl security team members during our work with the > 20160803A flaw during June 2016. We contacted distros@...nwall on July 31. > > libcurl 7.50.1 was released on August 3 2016, coordinated with the > publication of this advisory. > > CREDITS > ------- > > Found by the curl security team. Patch by Daniel Stenberg. > > Thanks a lot! View attachment "0001-nss-refuse-previously-loaded-certificate-from-file.patch" of type "text/x-patch" (1525 bytes)
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