Bug 1154059 – curl: Disable out-of-protocol fallback to SSL 3.0

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Bug 1154059 - curl: Disable out-of-protocol fallback to SSL 3.0

Summary:	curl: Disable out-of-protocol fallback to SSL 3.0

Status:	CLOSED ERRATA

Aliases:	None

Product:	Red Hat Enterprise Linux 6
Classification:	Red Hat
Component:	curl (Show other bugs)
Sub Component:
Version:	6.5
Hardware:	Unspecified Unspecified

Priority	high Severity high
Target Milestone:	rc
Target Release:	---
Assigned To:	Kamil Dudka
QA Contact:	Stefan Kremen
Docs Contact:

URL:
Whiteboard:
Keywords:

Depends On:	1154060
Blocks:	1159820 1159926
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Reported:	2014-10-17 08:26 EDT by Florian Weimer
Modified:	2015-07-22 01:43 EDT (History)
CC List:	6 users (show)

See Also:	CVE-2014-3566/POODLE
Fixed In Version:	curl-7.19.7-43.el6
Doc Type:	Deprecated Functionality
Doc Text:	Previously, libcurl implemented an out-of-protocol fallback to SSL 3.0 (Secure Sockets Layer) in order to securely communicate with TLS (Transport Layer Security) intolerant servers. This could have been abused by an attacker to force downgrade of the SSL version. Therefore, this feature has been removed from libcurl. Users of libcurl that have been relying on this feature are advised to explicitly enable SSL 3.0 by the --sslv3 option of curl (or the CURL_SSLVERSION_SSLv3 constant of libcurl API) to prevent connection failures when TLS intolerant servers are involved.
Story Points:	---
Clone Of:
Clones:	1154060 (view as bug list)
Environment:
Last Closed:	2015-07-22 01:43:47 EDT
Type:	Bug
Regression:	---
Mount Type:	---
Documentation:	---
CRM:
Verified Versions:
Category:	---
oVirt Team:	---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---

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External Trackers
Tracker	ID	Priority	Status	Summary	Last Updated
Red Hat Product Errata	RHSA-2015:1254	normal	SHIPPED_LIVE	Moderate: curl security, bug fix, and enhancement update	2015-07-20 13:50:03 EDT

Groups: None (edit)

Description Florian Weimer 2014-10-17 08:26:15 EDT

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 3 Tomas Hoger 2014-10-23 12:02:06 EDT

(In reply to Florian Weimer from comment #0)
> 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.

Or environment variable?  CURL_ENABLE_SSL_FALLBACK?

Do curl try to fall back across multiple versions (TLS 1.1 -> TLS 1.0 -> SSL 3.0), or if connection attempt with the highest supported fails, it goes straight to SSL 3.0?

Comment 4 Kamil Dudka 2014-10-23 12:06:58 EDT

(In reply to Tomas Hoger from comment #3)
> Or environment variable?  CURL_ENABLE_SSL_FALLBACK?

That would also work I guess.

> Do curl try to fall back across multiple versions (TLS 1.1 -> TLS 1.0 -> SSL
> 3.0), or if connection attempt with the highest supported fails, it goes
> straight to SSL 3.0?

The fallback implemented by libcurl goes straight to SSL 3.0.

Comment 12 errata-xmlrpc 2015-07-22 01:43:47 EDT

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.

https://rhn.redhat.com/errata/RHSA-2015-1254.html

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