Bug 1154060

Summary: curl: Disable out-of-protocol fallback to SSL 3.0
Product: Red Hat Enterprise Linux 7 Reporter: Florian Weimer <fweimer>
Component: curlAssignee: Kamil Dudka <kdudka>
Status: CLOSED ERRATA QA Contact: Stefan Kremen <skremen>
Severity: high Docs Contact:
Priority: high    
Version: 7.1CC: andy.fletcher, bressers, fweimer, john.haxby, kdudka, ksrot, mitr, ovasik, qe-baseos-security, skremen, thoger
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Fixed In Version: curl-7.29.0-24.el7 Doc Type: Deprecated Functionality
Doc Text:
An out-of-protocol fallback to SSL version 3.0 was available with libcurl. Attackers could abuse the fallback to force downgrade of the SSL version. The fallback has been removed from libcurl. Users requiring this functionality can explicitly enable SSL 3.0 through the libcurl API.
Story Points: ---
Clone Of: 1154059
: 1166567 (view as bug list) Environment:
Last Closed: 2015-11-19 07:06:48 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On: 1166567    
Bug Blocks: Red Hat1110700, 1154059, Red Hat1191021    

Description Florian Weimer 2014-10-17 12:28:07 UTC
+++ This bug was initially created as a clone of Bug #1154059 +++

We should disable the retry-with-SSL-3.0 behavior in curl because it can be trivially triggered by an on-path attacker to cause a protocol downgrade, and SSL 3.0 has several known weaknesses.  This curl behavior is quite surprising because it is restricted to the NSS backend, and other systems which use the OpenSSL or GNUTLS backend do not share this behavior.

At this stage, it is best to leave SSL 3.0 enabled.  (The in-protocol version negotiation has not been broken, sosome TLS version will be used automatically if supported by the server.)

This might reintroduce bug 525496 and bug 527771, so a system-wide knob to re-enable the SSL 3.0 fallback might be necessary.  Perhaps the existence of a file like /etc/sysconfig/curl/enable-ssl-fallback could re-enable the old behavior.

Comment 2 Kamil Dudka 2014-10-29 14:26:08 UTC
The code in question has been removed from upstream libcurl:


Comment 30 errata-xmlrpc 2015-11-19 07:06:48 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.