/usr/share/ssh/blacklist.DSA-2048 is in openssh-blacklist-extra 0.4.1+nmu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | # In the window of time that libssl had a weak key generator, openssh was
# no longer capable of generating DSA-2048 keys. As a result, this file
# is empty. This causes openssh-vulnkey to report that it knows about
# this key type/size and that there are correctly no matching keys.
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