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Insecure Randomness



GUID Versions

Version identification: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx The four-bit M and the 1- to 3-bit N fields code the format of the UUID itself.

Version Notes
0 Only 00000000-0000-0000-0000-000000000000
1 based on time, or clock sequence
2 reserved in the RFC 4122, but ommitted in many implementations
3 based on a MD5 hash
4 randomly generated
5 based on a SHA1 hash


  • intruder-io/guidtool - A tool to inspect and attack version 1 GUIDs
    $ guidtool -i 95f6e264-bb00-11ec-8833-00155d01ef00
    UUID version: 1
    UUID time: 2022-04-13 08:06:13.202186
    UUID timestamp: 138691299732021860
    UUID node: 91754721024
    UUID MAC address: 00:15:5d:01:ef:00
    UUID clock sequence: 2099
    $ guidtool 1b2d78d0-47cf-11ec-8d62-0ff591f2a37c -t '2021-11-17 18:03:17' -p 10000

Mongo ObjectId

Mongo ObjectIds are generated in a predictable manner, the 12-byte ObjectId value consists of: * Timestamp (4 bytes): Represents the ObjectId’s creation time, measured in seconds since the Unix epoch (January 1, 1970). * Machine Identifier (3 bytes): Identifies the machine on which the ObjectId was generated. Typically derived from the machine's hostname or IP address, making it predictable for documents created on the same machine. * Process ID (2 bytes): Identifies the process that generated the ObjectId. Typically the process ID of the MongoDB server process, making it predictable for documents created by the same process. * Counter (3 bytes): A unique counter value that is incremented for each new ObjectId generated. Initialized to a random value when the process starts, but subsequent values are predictable as they are generated in sequence.


  • andresriancho/mongo-objectid-predict - Predict Mongo ObjectIds
    ./mongo-objectid-predict 5ae9b90a2c144b9def01ec37


Last update: September 25, 2023