Bug 9581

OpenSSL Security Advisory [3rd May 2016]
========================================

Memory corruption in the ASN.1 encoder (CVE-2016-2108) ======================================================
Severity: High

This issue affected versions of OpenSSL prior to April 2015. The bug causing the vulnerability was fixed on April 18th 2015, and released as part of the June 11th 2015 security releases. The security impact of the bug was not known at the time.

In previous versions of OpenSSL, ASN.1 encoding the value zero represented as a negative integer can cause a buffer underflow with an out-of-bounds write in i2c_ASN1_INTEGER. The ASN.1 parser does not normally create "negative zeroes" when parsing ASN.1 input, and therefore, an attacker cannot trigger this bug.

However, a second, independent bug revealed that the ASN.1 parser (specifically, d2i_ASN1_TYPE) can misinterpret a large universal tag as a negative zero value. Large universal tags are not present in any common ASN.1 structures (such as X509) but are accepted as part of ANY structures.

Therefore, if an application deserializes untrusted ASN.1 structures containing an ANY field, and later reserializes them, an attacker may be able to trigger an out-of-bounds write. This has been shown to cause memory corruption that is potentially exploitable with some malloc implementations.

Applications that parse and re-encode X509 certificates are known to be vulnerable. Applications that verify RSA signatures on X509 certificates may also be vulnerable; however, only certificates with valid signatures trigger ASN.1 re-encoding and hence the bug. Specifically, since OpenSSL's default TLS X509 chain verification code verifies the certificate chain from root to leaf, TLS handshakes could only be targeted with valid certificates issued by trusted Certification Authorities.

OpenSSL 1.0.2 users should upgrade to 1.0.2c
OpenSSL 1.0.1 users should upgrade to 1.0.1o

This vulnerability is a combination of two bugs, neither of which individually has security impact. The first bug (mishandling of negative zero integers) was reported to OpenSSL by Huzaifa Sidhpurwala (Red Hat) and independently by Hanno B??ck in April 2015. The second issue (mishandling of large universal tags) was found using libFuzzer, and reported on the public issue tracker on March 1st 2016. The fact that these two issues combined present a security vulnerability was reported by David Benjamin (Google) on March 31st 2016. The fixes were developed by Steve Henson of the OpenSSL development team, and David Benjamin.  The OpenSSL team would also like to thank Mark Brand and Ian Beer from the Google Project Zero team for their careful analysis of the impact.

The fix for the "negative zero" memory corruption bug can be identified by commits

3661bb4e7934668bd99ca777ea8b30eedfafa871 (1.0.2) and 32d3b0f52f77ce86d53f38685336668d47c5bdfe (1.0.1)

Padding oracle in AES-NI CBC MAC check (CVE-2016-2107) ======================================================
Severity: High

A MITM attacker can use a padding oracle attack to decrypt traffic when the connection uses an AES CBC cipher and the server support AES-NI.

This issue was introduced as part of the fix for Lucky 13 padding attack (CVE-2013-0169). The padding check was rewritten to be in constant time by making sure that always the same bytes are read and compared against either the MAC or padding bytes. But it no longer checked that there was enough data to have both the MAC and padding bytes.

OpenSSL 1.0.2 users should upgrade to 1.0.2h
OpenSSL 1.0.1 users should upgrade to 1.0.1t

This issue was reported to OpenSSL on 13th of April 2016 by Juraj Somorovsky using TLS-Attacker. The fix was developed by Kurt Roeckx of the OpenSSL development team.

EVP_EncodeUpdate overflow (CVE-2016-2105) =========================================
Severity: Low

An overflow can occur in the EVP_EncodeUpdate() function which is used for

Base64 encoding of binary data. If an attacker is able to supply very large amounts of input data then a length check can overflow resulting in a heap corruption.

Internally to OpenSSL the EVP_EncodeUpdate() function is primarly used by the

PEM_write_bio* family of functions. These are mainly used within the OpenSSL command line applications. These internal uses are not considered vulnerable because all calls are bounded with length checks so no overflow is possible.

User applications that call these APIs directly with large amounts of untrusted data may be vulnerable. (Note: Initial analysis suggested that the

PEM_write_bio* were vulnerable, and this is reflected in the patch commit message. This is no longer believed to be the case).

OpenSSL 1.0.2 users should upgrade to 1.0.2h OpenSSL 1.0.1 users should upgrade to 1.0.1t

This issue was reported to OpenSSL on 3rd March 2016 by Guido Vranken. The fix was developed by Matt Caswell of the OpenSSL development team.


EVP_EncryptUpdate overflow (CVE-2016-2106) ==========================================
Severity: Low

An overflow can occur in the EVP_EncryptUpdate() function. If an attacker is able to supply very large amounts of input data after a previous call to

EVP_EncryptUpdate() with a partial block then a length check can overflow resulting in a heap corruption. Following an analysis of all OpenSSL internal usage of the EVP_EncryptUpdate() function all usage is one of two forms.

The first form is where the EVP_EncryptUpdate() call is known to be the first called function after an EVP_EncryptInit(), and therefore that specific call must be safe. The second form is where the length passed to EVP_EncryptUpdate() can be seen from the code to be some small value and therefore there is no possibility of an overflow. Since all instances are one of these two forms, it is believed that there can be no overflows in internal code due to this problem.

It should be noted that EVP_DecryptUpdate() can call EVP_EncryptUpdate() in certain code paths. Also EVP_CipherUpdate() is a synonym for EVP_EncryptUpdate(). All instances of these calls have also been analysed too and it is believed there are no instances in internal usage where an overflow could occur.

This could still represent a security issue for end user code that calls this function directly.

OpenSSL 1.0.2 users should upgrade to 1.0.2h
OpenSSL 1.0.1 users should upgrade to 1.0.1t

This issue was reported to OpenSSL on 3rd March 2016 by Guido Vranken. The fix was developed by Matt Caswell of the OpenSSL development team.

ASN.1 BIO excessive memory allocation (CVE-2016-2109) =====================================================
Severity: Low

When ASN.1 data is read from a BIO using functions such as d2i_CMS_bio() a short invalid encoding can casuse allocation of large amounts of memory potentially consuming excessive resources or exhausting memory.

Any application parsing untrusted data through d2i BIO functions is affected.

The memory based functions such as d2i_X509() are *not* affected. Since the memory based functions are used by the TLS library, TLS applications are not affected.

OpenSSL 1.0.2 users should upgrade to 1.0.2h
OpenSSL 1.0.1 users should upgrade to 1.0.1t

This issue was reported to OpenSSL on 4th April 2016 by Brian Carpenter.
The fix was developed by Stephen Henson of the OpenSSL development team.

EBCDIC overread (CVE-2016-2176)
===============================
Severity: Low

ASN1 Strings that are over 1024 bytes can cause an overread in applications using the X509_NAME_oneline() function on EBCDIC systems. This could result in arbitrary stack data being returned in the buffer.

OpenSSL 1.0.2 users should upgrade to 1.0.2h
OpenSSL 1.0.1 users should upgrade to 1.0.1t

This issue was reported to OpenSSL on 5th March 2016 by Guido Vranken. The fix was developed by Matt Caswell of the OpenSSL development team.

Note
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As per our previous announcements and our Release Strategy (https://www.openssl.org/policies/releasestrat.html), support for OpenSSL version 1.0.1 will cease on 31st December 2016. No security updates for that version will be provided after that date. Users of 1.0.1 are advised to upgrade.

Support for versions 0.9.8 and 1.0.0 ended on 31st December 2015. Those versions are no longer receiving security updates.

References
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URL for this Security Advisory:
https://www.openssl.org/news/secadv/20160503.txt

Note: the online version of the advisory may be updated with additional details over time.