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Sigurnosni nedostaci programskog paketa openssl

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FreeBSD-SA-16:12.openssl Security Advisory
The FreeBSD Project

Topic: Multiple OpenSSL vulnerabilities

Category: contrib
Module: openssl
Announced: 2016-03-10
Credits: OpenSSL Project
Affects: All supported versions of FreeBSD.
Corrected: 2016-03-04 00:40:15 UTC (stable/10, 10.2-BETA3)
2016-03-03 07:30:55 UTC (releng/10.2, 10.2-RELEASE-p13)
2016-03-03 07:30:55 UTC (releng/10.1, 10.1-RELEASE-p30)
2016-03-10 03:58:48 UTC (stable/9, 9.3-STABLE)
2016-03-10 10:03:28 UTC (releng/9.3, 9.3-RELEASE-p38)
CVE Name: CVE-2016-0702, CVE-2016-0703, CVE-2016-0704, CVE-2016-0705
CVE-2016-0797, CVE-2016-0798, CVE-2016-0799, CVE-2016-0800

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:>.

I. Background

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

A cross-protocol attack was discovered that could lead to decryption of TLS
sessions by using a server supporting SSLv2 and EXPORT cipher suites as a
Bleichenbacher RSA padding oracle. Note that traffic between clients and
non-vulnerable servers can be decrypted provided another server supporting
SSLv2 and EXPORT ciphers (even with a different protocol such as SMTP, IMAP
or POP3) shares the RSA keys of the non-vulnerable server. This vulnerability
is known as DROWN. [CVE-2016-0800]

A double free bug was discovered when OpenSSL parses malformed DSA private
keys and could lead to a DoS attack or memory corruption for applications that
receive DSA private keys from untrusted sources. This scenario is considered
rare. [CVE-2016-0705]

The SRP user database lookup method SRP_VBASE_get_by_user had confusing memory
management semantics; the returned pointer was sometimes newly allocated, and
sometimes owned by the callee. The calling code has no way of distinguishing
these two cases. [CVE-2016-0798]

In the BN_hex2bn function, the number of hex digits is calculated using an int
value |i|. Later |bn_expand| is called with a value of |i * 4|. For large
values of |i| this can result in |bn_expand| not allocating any memory because
|i * 4| is negative. This can leave the internal BIGNUM data field as NULL
leading to a subsequent NULL pointer dereference. For very large values of
|i|, the calculation |i * 4| could be a positive value smaller than |i|. In
this case memory is allocated to the internal BIGNUM data field, but it is
insufficiently sized leading to heap corruption. A similar issue exists in
BN_dec2bn. This could have security consequences if BN_hex2bn/BN_dec2bn is
ever called by user applications with very large untrusted hex/dec data. This
is anticipated to be a rare occurrence. [CVE-2016-0797]

The internal |fmtstr| function used in processing a “%s” formatted string in
the BIO_*printf functions could overflow while calculating the length of
a string and cause an out-of-bounds read when printing very long strings.

A side-channel attack was found which makes use of cache-bank conflicts on the
Intel Sandy-Bridge microarchitecture which could lead to the recovery of RSA
keys. [CVE-2016-0702]

s2_srvr.c did not enforce that clear-key-length is 0 for non-export ciphers.
If clear-key bytes are present for these ciphers, they displace encrypted-key
bytes. [CVE-2016-0703]

s2_srvr.c overwrites the wrong bytes in the master key when applying
Bleichenbacher protection for export cipher suites. [CVE-2016-0704]

III. Impact

Servers that have SSLv2 protocol enabled are vulnerable to the “DROWN” attack
which allows a remote attacker to fast attack many recorded TLS connections
made to the server, even when the client did not make any SSLv2 connections

An attacker who can supply malformed DSA private keys to OpenSSL applications
may be able to cause memory corruption which would lead to a Denial of
Service condition. [CVE-2016-0705]

An attacker connecting with an invalid username can cause memory leak, which
could eventually lead to a Denial of Service condition. [CVE-2016-0798]

An attacker who can inject malformed data into an application may be able
to cause memory corruption which would lead to a Denial of Service
condition. [CVE-2016-0797, CVE-2016-0799]

A local attacker who has control of code in a thread running on the same
hyper-threaded core as the victim thread which is performing decryptions
could recover RSA keys. [CVE-2016-0702]

An eavesdropper who can intercept SSLv2 handshake can conduct an efficient
divide-and-conquer key recovery attack and use the server as an oracle to
determine the SSLv2 master-key, using only 16 connections to the server
and negligible computation. [CVE-2016-0703]

An attacker can use the Bleichenbacher oracle, which enables more efficient
variant of the DROWN attack. [CVE-2016-0704]

IV. Workaround

No workaround is available.

V. Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

Restart all deamons using the library, or reboot the system.

2) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Restart all deamons using the library, or reboot the system.

3) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 9.3]
# fetch
# fetch
# gpg –verify openssl-9.3.patch.xz.asc

Note that the initial patch version contains a serious regression that
would lead to crash. The following patch must be applied to address it.

# fetch
# fetch
# gpg –verify openssl-9.3-fix.patch.asc

[FreeBSD 10.1]
# fetch
# fetch
# gpg –verify openssl-10.1.patch.xz.asc

[FreeBSD 10.2]
# fetch
# fetch
# gpg –verify openssl-10.2.patch.asc

b) Apply the patch. Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:>.

Restart all deamons using the library, or reboot the system.

VI. Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path Revision
– ————————————————————————-
stable/9/ r296598
releng/9.3/ r296611
stable/10/ r296371
releng/10.1/ r296341
releng/10.2/ r296341
– ————————————————————————-

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://

Or visit the following URL, replacing NNNNNN with the revision number:


VII. References










The latest revision of this advisory is available at
Version: GnuPG v2.1.11 (FreeBSD)

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AutorMarko Stanec
Cert idNCERT-REF-2016-03-0048-ADV
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