![]() ![]() With the above information in her possession, the attacker can now try to narrow down the set of possible valid identifiers to a size that’s feasible for a brute force attack. When starting the recovery on the victim account, she know precisely when she sends the request to the server.Sending such an email to her own account reveals the node identifier and the delay between sending the HTTP request to start the recovery process and the timestamp within the UUID.However, if an attacker is performing such an operation, she already has a few advantages. ![]() Version 1 UUIDs might sound like a good idea for some to generate the link. While MAC addresses are a form of information leak themselves (see the case of Microsoft Word w.r.t privacy), if the attacker already has a valid ID with the node identifier, it’s a lot easier to guess future UUIDs.Ī great example of this is an account recovery form, where a unique link is sent to the user’s email address, and clicking that link proves that whoever is trying to recover the account has access to the mailbox. On the other end of the spectrum is version 1, which contains a node identifier (typically the MAC address of the network card) and a timestamp. You can already see a big difference in how standard library designers treat this subject, as former offers a self-explanatory name, while latter depends on people knowing which version number 4 might refer to. This is what you get when you use the static randomUUID method of the class in Java, or the function uuid4 of the module uuid in Python. To start with a good example, version 4 UUIDs contain 122 random bits, so depending on the quality of the PRNG (Pseudo Random Number Generator), there’s a good chance that such identifiers are hard to predict. UUIDs come in different flavors, and depending on the version number, it might be easy or really difficult to guess the output of a UUID generator. Not everyone knows however, what these numbers represent. ![]()
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