GnuPG (version 2.5.21) for Windows contains a vulnerability where default Discretionary Access Control List (DACL) inheritance on the C:\ProgramData directory allows members of the BUILTIN\Users group to create arbitrary subdirectories under this path. An attacker with low-privilege access can create the expected GnuPG configuration directory and inject malicious configuration files consumed by GnuPG components. This can result in code execution within the security context of the victim user.
gpgtar in GnuPG before 2.5.19 can allow file overwrite via crafted data in an archive. When extracting an untrusted archive with --directory (aka -C) into an existing directory containing a pre-existing symlink, gpgtar can follow that symlink and create or overwrite a file outside the selected extraction directory. The write is limited by the extraction user's filesystem permissions. An archive extracted into a fresh empty directory does not have this risk.
In GnuPG before 2.4.9, armor_filter in g10/armor.c has two increments of an index variable where one is intended, leading to an out-of-bounds write for crafted input. (For ExtendedLTS, 2.2.51 and later are fixed versions.)
GnuPG can be made to spin on a relatively small input by (for example) crafting a public key with thousands of signatures attached, compressed down to just a few KB.