Let's check the attached file:

root@kali:/media/sf_CTFs/bsidestlv/TheTarget/TheTarget# file TheTarget
TheTarget: Extensible storage engine DataBase, version 0x620, checksum 0xbb95e8e9, page size 8192, Windows version 6.3

It's a 75MB ESE DB.

We can use libesedb to work with it. We just need to download the latest version from github, and call ./configure and make to built it from sources. (On Windows, we can use ESEDatabaseView).

First, we can check what are the tables contained within the DB:

[email protected]:/media/sf_CTFs/bsidestlv/TheTarget/TheTarget# ./libesedb-20200418/esedbtools/esedbinfo TheTarget | grep "Table: "
Table: 1                        MSysObjects (2)
Table: 2                        MSysObjectsShadow (3)
Table: 3                        MSysObjids (6)
Table: 4                        MSysLocales (7)
Table: 5                        datatable (8)
Table: 6                        hiddentable (185)
Table: 7                        link_history_table (186)
Table: 8                        link_table (194)
Table: 9                        quota_rebuild_progress_table (207)
Table: 10                       quota_table (208)
Table: 11                       sdpropcounttable (209)
Table: 12                       sdproptable (210)
Table: 13                       sd_table (214)

datatable sounds the most interesting, so let's dump it:

root@kali:/media/sf_CTFs/bsidestlv/TheTarget/TheTarget# ./libesedb-20200418/esedbtools/esedbexport -T datatable TheTarget
esedbexport 20200418

Opening file.
Database type: Unknown.
Exporting table 5 (datatable).
Export completed.

Now we just search for the flag format:

root@kali:/media/sf_CTFs/bsidestlv/TheTarget/TheTarget/TheTarget.export# sed 's/\x09/\x00/g' datatable.4 | strings | egrep -i "BSidesTLV(2020)?{"

(Note: For some reason, the export uses 0x09 as a filler character, we replace it with 0x00 for convenience).