2/2/2024 0 Comments Signal desktop![]() I wanted to ensure that this wasn’t specific to Windows, but being that the Signal Desktop Client has a shared codebase across operating systems, it probably wasn’t a Windows only vulnerability. Nonetheless, this vulnerability is another point of failure and makes it five times easier for unskilled adversaries to possibly recover sensitive information. Again though, we return back to the fact that the Signal Desktop Client stores the encryption key on disk anyway (lol). An adversary intelligence organization could pull the disk from a PC and take a snapshot, and recover all of these attachments, unencrypted. The other possible risk could be foreign emissaries being wrongfully detained and forcefully searched. The possible attack vector would be an adversary who already has local host access, looking to intercept your communications to recover secrets to pivot elsewhere in the environment or exploit external trust (such as passwords for third-party services). While true, this is just one less step to decrypt files, because…well you don’t have to decrypt them at all. When I discussed this vulnerability, several people had brought up the fact that Signal stores the decryption key on disk with the Desktop Client anyway. An adversary that can get their hands on these files wouldn’t even need to decrypt them and there’s no regular purging process, so undeleted files just sit unencrypted in this folder.Īs displayed, the file was successfully recovered, even after being deleted (and basically the reason I went on this wild chase to being with). ![]() In general, the cache mishandling opens up a slew of issues. If someone were to reply to the attachment, the file would not be cleared from the cache, thus CVE number one: Cleartext Storage of Sensitive Information (CVE-2023-24069) was born. ![]() However, there was one small edge case: replying to the attachment. After deleting the file, it was indeed purged from the %AppData% folder. īased on previous vulnerability research with Keybase, I then wondered if the image would properly get purged if I were to delete it. On this image in particular, you can see that the date is labeled as. This isn’t an edge case though, Signal is temporarily storing all of these attachments, unencrypted. png (on macOS and Linux you can see a preview of the native extensions so you don’t have to manually look at file properties) The image was stored as a regular file in this directory, and the image can be recovered by modifying the extension and adding. To replicate, an image was sent in a group chat C:\Users\foo\AppData\Roaming\Signal\attachments.noindex\*\ After looking through multiple files, the culprit directory was identified. ![]() Now, add the Signal repository to your system: echo "deb xenial main" | sudo tee -a /etc/apt//signal-xenial.While using signal, it was observed that the preview of an image was still visible even after having deleted the image because the image had been “replied” to. If you're running any of the following distros: Debian, Ubuntu, Linux Mint, and the likes, you can install Signal Desktop using APT.įirst, get the GPG keys using wget to safely download the Signal Desktop app: wget -O- | sudo apt-key add. Let's start with APT since it's the most preferred package manager of choice for most people and comes pre-installed on all major Linux distros. Once done, you are ready to install Signal Desktop on your Linux machine. However, if you're new to Signal, you'll have to download it on your mobile phone and set up an account using your phone number. If you're an existing Signal user, you probably already have the app on your Android or iOS device.
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