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Jo-Philipp Wich [Tue, 1 Mar 2016 14:31:08 +0000 (14:31 +0000)]

openssl: update to 1.0.2g (8 CVEs)

CVE-2016-0704

s2_srvr.c overwrite the wrong bytes in the master-key when applying
Bleichenbacher protection for export cipher suites. This provides a
Bleichenbacher oracle, and could potentially allow more efficient variants of
the DROWN attack.

CVE-2016-0703

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. This leads to an efficient divide-and-conquer key recovery attack: if
an eavesdropper has intercepted an SSLv2 handshake, they can use the server as
an oracle to determine the SSLv2 master-key, using only 16 connections to the
server and negligible computation. More importantly, this leads to a more
efficient version of DROWN that is effective against non-export ciphersuites,
and requires no significant computation.

CVE-2016-0702

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. The ability to exploit this issue is limited as it relies on an
attacker who has control of code in a thread running on the same hyper-
threaded core as the victim thread which is performing decryptions.

CVE-2016-0799

The internal |fmtstr| function used in processing a "%s" format string in
the BIO_*printf functions could overflow while calculating the length of a
string and cause an OOB read when printing very long strings. Additionally
the internal |doapr_outch| function can attempt to write to an OOB memory
location (at an offset from the NULL pointer) in the event of a memory
allocation failure. In 1.0.2 and below this could be caused where the size
of a buffer to be allocated is greater than INT_MAX. E.g. this could be in
processing a very long "%s" format string. Memory leaks can also occur.
The first issue may mask the second issue dependent on compiler behaviour.
These problems could enable attacks where large amounts of untrusted data is
passed to the BIO_*printf functions. If applications use these functions in
this way then they could be vulnerable. OpenSSL itself uses these functions
when printing out human-readable dumps of ASN.1 data. Therefore applications
that print this data could be vulnerable if the data is from untrusted sources.
OpenSSL command line applications could also be vulnerable where they print out
ASN.1 data, or if untrusted data is passed as command line arguments. Libssl is
not considered directly vulnerable. Additionally certificates etc received via
remote connections via libssl are also unlikely to be able to trigger these
issues because of message size limits enforced within libssl.

CVE-2016-0797

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 ptr deref. 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. All OpenSSL internal usage of these functions use data that
is not expected to be untrusted, e.g. config file data or application command
line arguments. If user developed applications generate config file data based
on untrusted data then it is possible that this could also lead to security
consequences. This is also anticipated to be rare.

CVE-2016-0798

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. Specifically, SRP servers that configure a secret seed to hide
valid login information are vulnerable to a memory leak: an attacker connecting
with an invalid username can cause a memory leak of around 300 bytes per
connection. Servers that do not configure SRP, or configure SRP but do not
configure a seed are not vulnerable. In Apache, the seed directive is known as
SSLSRPUnknownUserSeed. To mitigate the memory leak, the seed handling in
SRP_VBASE_get_by_user is now disabled even if the user has configured a seed.
Applications are advised to migrate to SRP_VBASE_get1_by_user. However, note
that OpenSSL makes no strong guarantees about the indistinguishability of valid
and invalid logins. In particular, computations are currently not carried out
in constant time.

CVE-2016-0705

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-2016-0800

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 POP)
shares the RSA keys of the non-vulnerable server. This vulnerability is known
as DROWN (CVE-2016-0800). Recovering one session key requires the attacker to
perform approximately 2^50 computation, as well as thousands of connections to
the affected server. A more efficient variant of the DROWN attack exists
against unpatched OpenSSL servers using versions that predate 1.0.2a, 1.0.1m,
1.0.0r and 0.9.8zf released on 19/Mar/2015 (see CVE-2016-0703 below). Users can
avoid this issue by disabling the SSLv2 protocol in all their SSL/TLS servers,
if they've not done so already. Disabling all SSLv2 ciphers is also sufficient,
provided the patches for CVE-2015-3197 (fixed in OpenSSL 1.0.1r and 1.0.2f)
have been deployed. Servers that have not disabled the SSLv2 protocol, and are
not patched for CVE-2015-3197 are vulnerable to DROWN even if all SSLv2
ciphers are nominally disabled, because malicious clients can force the use of
SSLv2 with EXPORT ciphers. OpenSSL 1.0.2g and 1.0.1s deploy the following
mitigation against DROWN: SSLv2 is now by default disabled at build-time.
Builds that are not configured with "enable-ssl2" will not support SSLv2.
Even if "enable-ssl2" is used, users who want to negotiate SSLv2 via the
version-flexible SSLv23_method() will need to explicitly call either of:
SSL_CTX_clear_options(ctx, SSL_OP_NO_SSLv2); or SSL_clear_options(ssl,
SSL_OP_NO_SSLv2); as appropriate. Even if either of those is used, or the
application explicitly uses the version-specific SSLv2_method() or its client
or server variants, SSLv2 ciphers vulnerable to exhaustive search key recovery
have been removed. Specifically, the SSLv2 40-bit EXPORT ciphers, and SSLv2
56-bit DES are no longer available. In addition, weak ciphers in SSLv3 and up
are now disabled in default builds of OpenSSL. Builds that are not configured
with "enable-weak-ssl-ciphers" will not provide any "EXPORT" or "LOW" strength
ciphers.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
SVN-Revision: 48868