Daniel Stenberg reported the following vulnerability in cURL:
libcurl incorrectly validates wildcard SSL certificates containing literal
RFC 2818 covers the requirements for matching Common Names (CNs) and
subjectAltNames in order to establish valid SSL connections. It first
discusses CNs that are for hostnames, and the rules for wildcards in this
case. The next paragraph in the RFC then discusses CNs that are IP
'In some cases, the URI is specified as an IP address rather than a
hostname. In this case, the iPAddress subjectAltName must be present in the
certificate and must exactly match the IP in the URI.'
The intention of the RFC is clear in that you should not be able to use
wildcards with IP addresses (in order to avoid the ability to perform
man-in-the-middle attacks). Unfortunately libcurl fails to adhere to this
rule under certain conditions, and subsequently it would allow and use a
wildcard match specified in the CN field.
Exploiting this flaw, a malicious server could participate in a MITM attack
or just easier fool users that it is a legitimate site for whatever purpose,
when it actually isn't.
A good CA should refuse to issue a certificate with the CN as indicated,
however there only need be one CA to issue one in error for this issue to
result in the user getting no warning at all and being vulnerable to MITM.
This flaw is only present in libcurl when built to use one out of a few
specific TLS libraries: OpenSSL, axtls, qsossl or gskit.
This problem is similar to the one previously reported by Richard Moore,
found in multiple browsers .
 http://www.westpoint.ltd.uk/advisories/wp-10-0001.txt (this is CVE-2010-3170)
Versions 7.1 to and including 7.35.0 are affected. The flaw is fixed in version 7.36.0
Red Hat would like to thank the cURL project for reporting this issue. Upstream acknowledges Richard Moore from Westpoint Ltd. as the original reporter.
Fixed now upstream in curl version 7.36.0.
Created mingw32-curl tracking bugs for this issue:
Affects: epel-5 [bug 1080891]
Created mingw-curl tracking bugs for this issue:
Affects: fedora-all [bug 1080880]
This issue did not affect the versions of curl as shipped with Red Hat Enterprise Linux 6 and 7 because it uses the NSS backend, not OpenSSL. It does affect Red Hat Enterprise Linux 5 which uses the OpenSSL backend.
Red Hat Enterprise Linux 5 is now in Production 3 Phase of the support and maintenance life cycle. This has been rated as having Low security impact and is not currently planned to be addressed in future updates. For additional information, refer to the Red Hat Enterprise Linux Life Cycle: https://access.redhat.com/support/policy/updates/errata/.
It seems this also affects lftp and is fixed in 4.6.2: