(FreeBSD Issues Fix) OpenSSL Alternative Certificate Chain Validation Flaw Lets Remote Users Forge Certificates
SecurityTracker Alert ID: 1032818|
SecurityTracker URL: http://securitytracker.com/id/1032818
(Links to External Site)
Date: Jul 9 2015
Modification of authentication information|
Fix Available: Yes Vendor Confirmed: Yes |
Version(s): 1.0.1o, 1.0.1n, 1.0.2b, 1.0.2c|
A vulnerability was reported in OpenSSL. A remote user can bypass certificate validation on the target system.|
When the validation of a certificate chain fails, the system attempts to validate an alternate certificate chain but does not check the CA flag of untrusted certificates. As a result, a remote user can cause the target system to validate an invalid certificate using a valid leaf certificate.
Applications that verify certificates are affected.
SSL/TLS/DTLS clients and SSL/TLS/DTLS servers using client authentication are affected.
The vendor was notified on June 24, 2015.
Adam Langley/David Benjamin (Google/BoringSSL) reported this vulnerability.
A remote user can bypass certificate validation on the target system.|
FreeBSD has issued a fix (10.2-PRERELEASE, 10.2-BETA1).|
FreeBSD 10.1-RELEASE is not affected.
The FreeBSD advisory is available at:
Vendor URL: security.FreeBSD.org/advisories/FreeBSD-SA-15:12.openssl.asc (Links to External Site)
|Underlying OS: UNIX (FreeBSD)|
|Underlying OS Comments: 10.1-STABLE|
This archive entry is a follow-up to the message listed below.|
Source Message Contents
Subject: FreeBSD Security Advisory FreeBSD-SA-15:12.openssl|
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FreeBSD-SA-15:12.openssl Security Advisory
The FreeBSD Project
Topic: OpenSSL alternate chains certificate forgery vulnerability
Credits: Adam Langley/David Benjamin (Google/BoringSSL), OpenSSL
Affects: FreeBSD 10.1-STABLE after 2015-06-11 and prior to the
Corrected: 2015-07-09 17:17:22 UTC (stable/10, 10.2-PRERELEASE,
CVE Name: CVE-2015-1793
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.
FreeBSD includes software from the OpenSSL Project. The OpenSSL Project is
a collaborative effort to develop a robust, commercial-grade, full-featured
Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3)
and Transport Layer Security (TLS v1) protocols as well as a full-strength
general purpose cryptography library.
II. Problem Description
During certificate verification, OpenSSL will attempt to find an alternative
certificate chain if the first attempt to build such a chain fails, unless
the application explicitly specifies X509_V_FLAG_NO_ALT_CHAINS.
An error in the implementation of this logic could erroneously mark
certificate as trusted when they should not.
An attacker could cause certain checks on untrusted certificates, such as the
CA (certificate authority) flag, to be bypassed, which would enable them to
use a valid leaf certificate to act as a CA and issue an invalid certificate.
No workaround is available.
NOTE WELL: This issue does not affect earlier FreeBSD releases, including the
supported 8.4, 9.3 and 10.1-RELEASE because the alternative certificate chain
feature was not introduced in these releases. Only 10.1-STABLE after
2015-06-11 and prior to the correction date is affected.
Upgrade your vulnerable system to the latest supported FreeBSD stable/10
branch dated after the correction date.
Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.
Restart all deamons using the library, or reboot the system.
VI. Correction details
The following list contains the correction revision numbers for each
To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:
# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
Or visit the following URL, replacing NNNNNN with the revision number:
The latest revision of this advisory is available at
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