Apple last week patched a security certificate flaw in iOS that could let hackers with a "privileged network position" crack an encrypted session and capture data, without the enduser realizing anything is wrong.
The weakness lies in the way iOS validates, or doesn't, the chain of trusted interactions involved in issuing and managing X.509 certificates in public key infrastructure (PKI) systems. The certificates are used in encrypting a user's data session. Apple's fix is available now in iOS 4.3.5, an update specifically to address this flaw.
The bug was found and reported by Paul Kehrer, SSL architect for Trustwave, a Chicago-based security software company, and published last week by the company's SpiderLabs incident response team.
One corporate iOS user is Needham Bank, a community bank in Needham, Mass. Nearly one-third of the bank's 100 or so employees have an iOS device, many of them iPads. The bank relies on SSL certificates to secure iOS communications. But the bank's vice president of IT, James Gordon, isn't sweating the update.
"We utilized MobileIron [a mobile device management application from MobileIron] to flag old [iOS] versions and stop the sync," says Gordon. "It instructs users to update. Once the [OS] updates, and their device is compliant, then we let the email and corporate apps sync."
Kehrer (Twitter: @reaperhulk) hit upon a way to sign an SSL certificate that iOS would see as a valid signature. If he could intercept traffic from an iOS device, say one connected to a Wi-Fi network, he could create his own SSL certificate, and then capture and decrypt the traffic packets. Ideally, for the attacker, the victim is not alerted to any problem so the attack goes undetected.
"This method allows for transparent man-in-the-middle attacks against encrypted iOS communications," according to TrustWave's security advisory.
For corporate users, the incident underlies the need to ensure iOS devices are forced to upgrade as soon as possible, often via a third-party device management application. [see "Gartner: How to get a handle on mobile device management"]
Apple's bland official description of the flaw doesn't quite do justice to the certificate flaw, and at least some users are stumbling on its potential seriousness almost accidentally.
That was the case for Cimarron Buser, vice president of products and marketing, at Apperian, a Boston software company that offers cloud-based mobile app management platform for iOS. He was meeting with some security experts who gave him an update on the issue, and he blogged about what he learned.
"At issue was Apple's 'core code' that checks certificate chain validation," he writes. "It was based on a 9-year old code base that had never been updated. And until now, no one had really worried about it."
His contacts described the problem: "Specifically, iOS's SSL certificate parsing contained a flaw where it failed to check the 'basicConstraints' parameter of certificates in the chain. So, by signing a new certificate using a legitimate end-entity certificate, an attacker could obtain a 'valid' certificate for any domain."
The 4.3.5 update corrects this "through improved validation of X.509 certificate chains," according to Apple.