Unsigned apps can dump the full OS keychain, including your plaintext passwords

Hackers can steal macOS keychain passwords using unsigned applications, it works on the latest version of macOS, High Sierra 10.13, and previous releases.

The cyber security expert Patrick Wardle, director of research at Synack, revealed that unsigned applications can steal macOS Keychain passwords from the latest version of macOS High Sierra and previous versions of macOS.

The researchers tested the exploit on Sierra and High Sierra, but he confirmed that El Capitan appears vulnerable as well. This issue is not a ‘High Sierra specific’ vulnerability.

The researchers shared a video that shows how an unsigned application can exfiltrate sensitive data from the macOS Keychain, including plaintext passwords.

“What does your attack do?
A: I discovered a flaw where malicious non-privileged code (or apps) could programmatically access the keychain and dump all this data …. including your plain text passwords. This is not something that is supposed to happen! :(” explained Wardle.

It interesting to note that the attack does not require root permissions. The attack does require the knowledge of the master password, it only needs the targeted user to download and launched a malicious application, clearly ignoring the warnings displayed when an app from an unidentified developer is being executed.

“Q: What are the prerequisites for this attack?
A: As this is a local attack, this means a hacker or piece of malware must first infect your your Mac! Typical ways to accomplish this include emails (with malicious attachments),  fake web popups (“your Flash player needs updating”), or sometimes legitimate application websites are hacked (e.g. Transmission, Handbrake, etc). Theoretically, this attack would be added as a capability or as a payload of such malware. For example, the malware would persist, survey the system, then use this attack to dump the keychain. If I was writing a modular mac backdoor or implant, I’d call it the “dump keychain” plugin :)”  added the expert.

Wardle reported the discovery to Apple along with a proof-of-concept (PoC) code, he avoided to publicly disclose technical details to prevent malicious actors from abusing the technique.

Security experts always recommend customers to download applications only from trusted sources and pay attention to the security warnings displayed by the operating system.

“A few things. As mentioned before, this attack is local, meaning malicious adversaries have to  first compromise your mac in some way. So best bet – don’t get infected. This means run the latest version of macOS and don’t run random apps from emails or the web. Also, this attack requires that the keychain is unlocked. By default the keychain is unlocked when the user logs in. However, you can change the keychain password (so it is not automatically unlocked during login, or (via the Keychain Access app) lock the keychain while you are not using it. ” suggests Wardle to stay safe.

Unfortunately, Apple’s bug bounty program doesn’t cover macOS., this means that the expert will not be rewarded … let me hope that Apple will make an exception in this case.

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Pierluigi Paganini

(Security Affairs – OS keychain, hacking)

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