While almost all the attention paid to the HTTPS-crippling FREAK vulnerability has focused on browsers, consider this: thousands of Android and iOS apps, many with finance, shopping, and medical uses, are also vulnerable to the same exploit that decrypts passwords, credit card details, and other sensitive data sent between handsets and Internet servers.

Security researchers from FireEye recently examined the most popular apps on Google Play and the Apple App Store and found 1,999 titles that left users wide open to the encryption downgrade attack. Specifically, 1,228 Android apps with one million or more downloads were vulnerable, while 771 out of the top 14,079 iOS apps were susceptible. Vulnerable apps were those that used—or in the case of iOS, could use—an affected crypto library and connected to servers that offered weak, 512-bit encryption keys. The number of vulnerable apps would no doubt mushroom when analyzing slightly less popular titles.

"As an example, an attacker can use a FREAK attack against a popular shopping app to steal a user's login credentials and credit card information," FireEye researchers Yulong Zhang, Zhaofeng Chen, Hui Xue, and Tao Wei wrote in a blog post published Tuesday afternoon. "Other sensitive apps include medical apps, productivity apps and finance apps." The researchers provided the screenshots above and below, which reveal the plaintext data extracted from one of the vulnerable apps after it connected to its paired server.

FREAK is a remnant of the 1990s, when the Clinton administration required weak keys to be used in any software or hardware that was exported out of the US. To comply, many software makers configured their products to offer 512-bit keys when used abroad. Many engineers abandoned the regimen once the restrictions were dropped, but a surprising number of HTTPS-supporting Web servers—estimated at 36 percent two weeks ago and 10 percent last week —continued to offer them.

When these servers connect to vulnerable end-user devices, attackers with the ability to monitor a connection—say someone on an unsecured Wi-Fi network or a rogue employee at an Internet service provider—can capitalize on the vulnerability. By injecting malicious packets into the flow, the attacker can first cause the two parties to use a weak 512-bit encryption key while negotiating encrypted Web sessions. The adversary can then collect some of the resulting exchange and use cloud-based computing from Amazon or other services to factor the website's underlying private key. From that point on, the attacker can masquerade as the official website, a coup that allows the data to be read or modified as it passes between the site and the end user over the unsecured network.

While Apple has patched iOS 8.2 against FREAK, the 771 App Store apps identified by FireEye remain vulnerable on iPhones and iPads that run earlier iOS versions. What's more, seven of the 771 apps are susceptible to FREAK attacks even when running the latest version, FireEye said. The FireEye researchers didn't identify the vulnerable apps. Android and iOS users should contact specific app makers to find out if their wares are affected. To test if browsers are vulnerable, visit this page. This SSLLabs page will test if a server offers weak, 512-bit keys.

Post updated add last two sentences and a link to the FireEye blog post and to change "hits" to "affects" in the headline.