OpenSSL Patches Five Flaws, Adds Protection Against Logjam Attack

Posted on

The OpenSSL project has patched several moderate- and low-severity security vulnerabilities and also has added protection against the Logjam attack in new releases of the software.

Most of the vulnerabilities fixed in the new releases are denial-of-service bugs, but one of them can potentially cause memory corruption. That vulnerability only affected older versions of OpenSSL.

If a DTLS peer receives application data between the ChangeCipherSpec and Finished messages, buffering of such data may cause an invalid free, resulting in a segmentation fault or potentially,  memory corruption. This issue affected older OpenSSL versions 1.0.1, 1.0.0 and 0.9.8,” the OpenSSL advisory says.

In addition to the patches, the new versions of OpenSSL also include protection against the Logjam attack, which was disclosed in May. That attack involves the way that servers handle the Diffie-Hellman key exchange.

OpenSSL Patches Five Flaws, Adds Protection Against Logjam Attack
OpenSSL Patches Five Flaws, Adds Protection Against Logjam Attack

“Millions of HTTPS, SSH, and VPN servers all use the same prime numbers for Diffie-Hellman key exchange. Practitioners believed this was safe as long as new key exchange messages were generated for every connection. However, the first step in the number field sieve—the most efficient algorithm for breaking a Diffie-Hellman connection—is dependent only on this prime. After this first step, an attacker can quickly break individual connections,” says an explanation of the vulnerability and attack, which was researched by a group of academic and industry experts from Johns Hopkins University, Microsoft, the University of Michigan and elsewhere. 

OpenSSL has added protection against the attack in version 1.0.2b and 1.0.1n.

“A vulnerability in the TLS protocol allows a man-in-the-middle attacker to downgrade vulnerable TLS connections using ephemeral Diffie-Hellman key exchange to 512-bit export-grade cryptography. This vulnerability is known as Logjam (CVE-2015-4000). OpenSSL has added protection for TLS clients by rejecting handshakes with DH parameters shorter than 768 bits. This limit will be increased to 1024 bits in a future release,” the advisory says.

The new releases also fix an exploitable issue that could allow an attacker to create malformed certificates and CRLs.

“X509_cmp_time does not properly check the length of the ASN1_TIME string and can read a few bytes out of bounds. In addition, X509_cmp_time accepts an arbitrary number of fractional seconds in the time string. An attacker can use this to craft malformed certificates and CRLs of various sizes and potentially cause a segmentation fault, resulting in a DoS on applications that verify certificates or CRLs. TLS clients that verify CRLs are affected. TLS clients and servers with client authentication enabled may be affected if they use custom verification callbacks,” the advisory says.



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s