Are there any known exploits in Signal's encryption protocol that could lead to messages being decrypted, or any other compromising information being released?

2 Answers 2


No, there are no known public flaw in Signal at the time of writing of this answer.

Source: there was only one CVE for Signal (for Android), in 2018. The only one listed (fixed in version 4.25.0 the 14 Aug 2018) could leak photos attached to disappearing messages.


It's not so much a flaw but more an expected and documented but nonetheless surprising behavior: since Signal uses the phone number as an ID, it is possible to identify whether a Signal account tied to a specific phone number is a member of a group that you are yourself a member of.

This has apparently been used by Chinese government agencies to identify dissidents:

  1. Get yourself added to the "subversive" group chat.
  2. Check a list of suspected dissident's phone numbers against the members of the group.

[I can't find the article nor remember the details, so I'm leaving this as a community wiki. If someone knows the details, please feel free to edit.]

  • 1
    Is this a weakness, though? If you are a member of a group, it's not a weakness that other members know who you are. Sure, it could be architected differently, but I wouldn't call this a weakness of the protocol.
    – schroeder
    Jan 19, 2021 at 9:20
  • @schroeder "or any other compromising information being released"
    – psitae
    Jan 20, 2021 at 18:47
  • @psitae then you might need to define what you mean, because the identity of those you are communicating with is not "compromising information". Neither is it a "flaw". Your question is now sounding like "tell me all the potentially bad things about Signal".
    – schroeder
    Jan 20, 2021 at 18:56
  • This is not an "exploit in Signal's encryption protocol"
    – Herohtar
    Jan 6 at 17:16

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