ASA-2019-00658 – Linux kernel: Mounting a crafted btrfs filesystem image can lead to a use-after-free through syncfs system call

Mounting a crafted btrfs filesystem image, performing some operations, and then making a syncfs system call can lead to a use-after-free in try_merge_free_space in fs/btrfs/free-space-cache.c because the pointer to a left data structure can be the same as the pointer to a right data structure.

ASA-2019-00657 – Linux kernel: Use-after-free vulnerability when deleting a file from a recently unmounted specially crafted ext4 filesystem

A flaw was found in the Linux kernel's ext4_unlink function. An attacker could corrupt memory or escalate privileges when deleting a file from a recently unmounted specially crafted ext4 filesystem, including local, USB, and iSCSI.

ASA-2019-00653 – OpenBSD: Local privilege escalation via S/Key and YubiKey

OpenBSD, in a non-default configuration where S/Key or YubiKey authentication is enabled, allows local users to become root by leveraging membership in the auth group. This occurs because root's file can be written to /etc/skey or /var/db/yubikey, and need not be owned by root.

ASA-2019-00652 – OpenBSD: libc’s authentication layer performed insufficient username validation

libc in OpenBSD allows authentication bypass via the -schallenge username, as demonstrated by smtpd, ldapd, or radiusd. This is related to gen/auth_subr.c and gen/authenticate.c in libc (and login/login.c and xenocara/app/xenodm/greeter/verify.c).