Pierluigi Paganini
March 08, 2022
Security expert Max Kellermann discovered a Linux flaw, dubbed Dirty Pipe and tracked as CVE-2022-0847, that can allow local users to gain root privileges on all major distros.
The vulnerability affects Linux Kernel 5.8 and later versions.
The CVE-2022-0847 vulnerability allows overwriting data in arbitrary read-only files, which could lead to privilege escalation because unprivileged processes can inject code into root processes.
Kellerman explained that the flaw is similar to CVE-2016-5195, aka Dirty Cow, and is more dangerous because it is easier to exploit.
In a blog post, the researcher explained that he discovered the flaw while investigating corrupt access log files for one of its customers.
Kellerman published technical details about the Dirty Pipe flaw along with a proof-of-concept (PoC) exploit that allows local users to overwrite any file contents in the page cache, even if the file is not permitted to be written, immutable or on a read-only mount.
BleepingComputer reported a tweet published by the security researcher Phith0n who explained that it is possible to use the exploit to modify the /etc/passwd file to set the root user without a password. Using this trick a non-privileged user could execute the command ‘su root’ to gain access to the root account.
Why did I overwrite the /etc/passwd?
— Phith0n (@phithon_xg) March 7, 2022
Because this file saves all the user information on Linux.
I remove the "x" flag behind the "root" user, it means that I set an empty password for this user. So I can use "su root" to escalate privilege without credentials.
The researcher Phith0n also published an updated version of the exploit that allows gaining root privileges by overwriting a SUID program like ./exp /usr/bin/su to drop a root shell at /tmp/sh and then executing the script.
Below is the timeline for this vulnerability:
Servers running outdated kernel versions are exposed to attacks exploiting this flaw.
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(SecurityAffairs – hacking, Linux)
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