POODLE Attacks Also Work Against TLS: Researchers

Communications encrypted with the transport layer security (TLS) protocol are also vulnerable to Padding Oracle On Downgraded Legacy Encryption (POODLE) attacks, researchers said on Monday.

In mid-October, researchers warned that communications encrypted with secure sockets layer (SSL) 3.0 are exposed to POODLE attacks due to a cipher block chaining (CBC) weakness (CVE-2014-3566) in the cryptographic protocol. After the news broke, many major companies started updating their products to protect customers against such attacks, including Google, Mozilla, Microsoft, Apple and Cisco.

Experts noted in October that TLS might also be susceptible to POODLE, and Google security engineer Adam Langley confirmed the reports on Monday.

“We’re removing SSLv3 in favour of TLS because TLS fully specifies the contents of the padding bytes and thus stops the attack,” Langley explained in a blog post. “However, TLS’s padding is a subset of SSLv3’s padding so, technically, you could use an SSLv3 decoding function with TLS and it would still work fine. It wouldn’t check the padding bytes but that wouldn’t cause any problems in normal operation. However, if an SSLv3 decoding function was used with TLS, then the POODLE attack would work, even against TLS connections.”

Langley has built a scanner that identifies the issue and found several major websites that are affected. After a closer analysis, the expert determined that the sites were vulnerable to POODLE because they had been using load balancers from F5 Networks and A10 Networks. The security engineer attempted to notify both companies immediately, but he couldn’t reach A10 Networks until mid-November.

On Monday, both F5 Networks and A10 Networks released software updates to address the flaw which has been assigned the CVE identifier CVE-2014-8730. Langley says products from other vendors might also be impacted, but hopefully they’ll take action to fix the vulnerability now that the news is out.

Qualys has updated its SSL Server Test website to help website owners determine if they are affected.

“The main target are browsers, because the attacker must inject malicious JavaScript to initiate the attack. A successful attack will use about 256 requests to uncover one cookie character, or only 4096 requests for a 16-character cookie. This makes the attack quite practical,” noted Ivan Ristic, director of engineering at Qualys.

According to Ristic, approximately 10% of the servers analyzed by his company are vulnerable.