Bug 1154060 - curl: Disable out-of-protocol fallback to SSL 3.0
Summary: curl: Disable out-of-protocol fallback to SSL 3.0
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: curl
Version: 7.1
Hardware: Unspecified
OS: Unspecified
Target Milestone: rc
: ---
Assignee: Kamil Dudka
QA Contact: Stefan Kremen
Depends On: 1166567
Blocks: 1110700 1154059 1191021
TreeView+ depends on / blocked
Reported: 2014-10-17 12:28 UTC by Florian Weimer
Modified: 2015-11-19 07:06 UTC (History)
11 users (show)

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.
Clone Of: 1154059
: 1166567 (view as bug list)
Last Closed: 2015-11-19 07:06:48 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Red Hat Bugzilla 1152789 0 high CLOSED CVE-2014-3566 SSL/TLS: Padding Oracle On Downgraded Legacy Encryption attack 2021-12-10 14:25:57 UTC
Red Hat Product Errata RHSA-2015:2159 0 normal SHIPPED_LIVE Moderate: curl security, bug fix, and enhancement update 2015-11-19 08:26:18 UTC

Internal Links: 1152789

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.


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