OpenSSL Patches Flaws Found With Google Fuzzer

OpenSSL updates released on Thursday patch two low and medium severity vulnerabilities discovered using Google’s open source OSS-Fuzz fuzzing service.

The medium severity flaw patched with the release of OpenSSL 1.1.0g and 1.0.2m is CVE-2017-3736. Described as a carry propagating bug in the x86_64 Montgomery squaring procedure, the security hole affects processors that support BMI1, BMI2 and ADX extensions (e.g. Intel Broadwell 5th generation and later, or AMD Ryzen).

These types of flaws could allow an attacker to recover encryption keys and access protected communications, but OpenSSL developers believe an attack is difficult to carry out.

“Analysis suggests that attacks against RSA and DSA as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH are considered just feasible (although very difficult) because most of the work necessary to deduce information about a private key may be performed offline,” OpenSSL said in an advisory.

“The amount of resources required for such an attack would be very significant and likely only accessible to a limited number of attackers. An attacker would additionally need online access to an unpatched system using the target private key in a scenario with persistent DH parameters and a private key that is shared between multiple clients,” it added.

Developers pointed out that the vulnerability is very similar to CVE-2015-3193, which was patched in December 2015, and CVE-2017-3732, one of the four security holes fixed this January. However, they believe CVE-2017-3736 needs to be treated separately.

The second vulnerability patched with the release of OpenSSL 1.1.0g and 1.0.2m is a low severity issue that could lead to an out-of-bounds (OOB) read. The flaw, tracked as CVE-2017-3735, has existed since 2006 and it was disclosed in August. While a source code fix was made available in August, developers believed it did not deserve an update due to its low severity.

The flaws resolved in the latest versions of OpenSSL were discovered using OSS-Fuzz, an open source fuzzing service launched by Google in December 2016. In the first months, the fuzzer helped find 264 potential security issues in 47 open source projects.

This is the fourth round of OpenSSL updates released this year, but only two of the previous updates, from January and February, included security patches.