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.)

In GnuPG through 2.4.8, if a signed message has \f at the end of a plaintext line, an adversary can construct a modified message that places additional text after the signed material, such that signature verification of the modified message succeeds (although an "invalid armor" message is printed during verification). This is related to use of \f as a marker to denote truncation of a long plaintext line.

In GnuPG before 2.5.5, if a user chooses to import a certificate with certain crafted subkey data that lacks a valid backsig or that has incorrect usage flags, the user loses the ability to verify signatures made from certain other signing keys, aka a "verification DoS."

GnuPG through 2.3.6, in unusual situations where an attacker possesses any secret-key information from a victim's keyring and other constraints (e.g., use of GPGME) are met, allows signature forgery via injection into the status line.

A flaw was found in the way certificate signatures could be forged using collisions found in the SHA-1 algorithm. An attacker could use this weakness to create forged certificate signatures. This issue affects GnuPG versions before 2.2.18.

Interaction between the sks-keyserver code through 1.2.0 of the SKS keyserver network, and GnuPG through 2.2.16, makes it risky to have a GnuPG keyserver configuration line referring to a host on the SKS keyserver network. Retrieving data from this network may cause a persistent denial of service, because of a Certificate Spamming Attack.

mainproc.c in GnuPG before 2.2.8 mishandles the original filename during decryption and verification actions, which allows remote attackers to spoof the output that GnuPG sends on file descriptor 2 to other programs that use the "--status-fd 2" option. For example, the OpenPGP data might represent an original filename that contains line feed characters in conjunction with GOODSIG or VALIDSIG status codes.

The keyring DB in GnuPG before 2.1.2 does not properly handle invalid packets, which allows remote attackers to cause a denial of service (invalid read and use-after-free) via a crafted keyring file.

dirmngr before 2.1.0 improperly handles certain system calls, which allows remote attackers to cause a denial of service (DOS) via a specially-crafted certificate.

parse-packet.c in GnuPG (gpg) 1.4.3 and 1.9.20, and earlier versions, allows remote attackers to cause a denial of service (gpg crash) and possibly overwrite memory via a message packet with a large length (long user ID string), which could lead to an integer overflow, as demonstrated using the --no-armor option.