A subtle mistake in how Apple implemented a basic encryption feature that shields data from snooping also affects many desktop applications that rely on the code, according to a noted security researcher.

Apple released a patch on Friday for its iOS mobile platform but has yet to fix the problem for desktop computers, which often have several applications that rely on the faulty code library, called Secure Transport.

Ashkan Soltani, an independent privacy and security researcher, said many other Apple and non-Apple applications are affected.

Security researcher Ashkan Soltani said several other desktop applications, include Apple’s Mail, FaceTime and Calendar, use a code library that could allow an attacker to steal data. (Click to enlarge.)

Those include Apple’s Mail, FaceTime, Calendar, Keynote, the Safari browser, iBooks and its Software Update applications. It would also appear to affect third-party applications, such as the desktop Twitter application and possibly VPN (virtual private network) connections, depending on their configurations, Soltani said.

The Secure Transport library, which handles setting up an encrypted connection for many applications, was contained in iOS 6 and up and OSX versions 10.9 and up, Soltani said via email.

Most websites handling sensitive personal data use SSL (Secure Sockets Layer) or TLS (Transport Layer Security), which establishes an encrypted connection between a server and a person’s computer. If an attacker intercepts the data, it is unreadable.

Apple’s mistake in Secure Transport allows an attacker to perform a man-in-middle attack, and supply fake data that makes it appear an authentic web service has been cryptographically verified.

“This enables an adversary to masquerade as coming from a trusted remote endpoint, such as your favorite webmail provider and perform full interception of encrypted traffic between you and the destination server,” wrote Alex Radocea, senior engineer with the computer security firm CrowdStrike, on Friday. CrowdStrike analyzed Apple’s patch for iOS after it was released.

The flaw is deeply buried in a line of code, wrote Adam Langley, a software engineer at Google, on his personal blog.

“This sort of subtle bug deep in the code is a nightmare,” Langley wrote. “I believe that it’s just a mistake and I feel very bad for whomever might have slipped in an editor and created it.

Until Apple fixes it, any data transmitted by those applications is at risk, although the danger is mitigated somewhat since an attacker must be on the same network as the victim.

Third-party application developers could tweak their code to use other SSL/TLS libraries, such as OpenSSL, but Apple is likely to fix the issue quickly.

“I suspect Apple should be pushing out a patch any day now,” Soltani said.