CVE-2024-21626: runc vulnerable to container breakout through process.cwd trickery and leaked fds

In runc 1.1.11 and earlier, due to an internal file descriptor leak, an attacker could cause a newly-spawned container process (from runc exec) to have a working directory in the host filesystem namespace, allowing for a container escape by giving access to the host filesystem (“attack 2”). The same attack could be used by a malicious image to allow a container process to gain access to the host filesystem through runc run (“attack 1”). Variants of attacks 1 and 2 could be also be used to overwrite semi-arbitrary host binaries, allowing for complete container escapes (“attack 3a” and “attack 3b”).

Strictly speaking, while attack 3a is the most severe from a CVSS perspective, attacks 2 and 3b are arguably more dangerous in practice because they allow for a breakout from inside a container as opposed to requiring a user execute a malicious image. The reason attacks 1 and 3a are scored higher is because being able to socially engineer users is treated as a given for UI:R vectors, despite attacks 2 and 3b requiring far more minimal user interaction (just reasonable runc exec operations on a container the attacker has access to). In any case, all four attacks can lead to full control of the host system.