It works by enabling attackers to misuse the alloca() function in a way that would result in memory corruption. This, in turn, allows a hacker to crash systemd and hence the entire operating system. Practically speaking, this can be done by a local attacker mounting a filesystem on a very long path. This causes too much memory space to be used in the systemd stack, which results in a system crash. That’s the bad news. The good news is that Red Hat Product Security and systemd’s developers have immediately patched the hole.
Qualys has discovered a new systemd security bug that enables any unprivileged user to cause a denial of service via a kernel panic. Slashdot reader inode_buddha shares the news via ZDNet’s Steven J. Vaughan-Nichols: As Bharat Jogi, Qualys’s senior manager of Vulnerabilities and Signatures, wrote, “Given the breadth of the attack surface for this vulnerability, Qualys recommends users apply patches for this vulnerability immediately.” You can say that again. Systemd is used in almost all modern Linux distributions. This particular security hole arrived in the systemd code in April 2015.