copyfail-alpine

This is a more minimal port of Copy Fail LPE (CVE-2026-31431) which patches the first few bytes of /etc/passwd so that su-ing to root requires no password. This reduces the total size of the original exploit and makes it more portable. Distributions like Alpine use busybox/musl instead of a standalone su binary and glibc linkage, so the original binary patching method generally doesn't work. I specifically wanted to make a port that works on Alpine, but this method should work on just about any distro with a vulnerable kernel independent of the underlying coreutil format and cpu architecture since it relies on modifying a more ubiquitous target. (note this poc is not a container escape)

Use the Go implementation for a portable standalone binary:

go build -o exp main.go
./exp

Or simply run the python script as an unprivileged user using python3 exp.py and enjoy your root shell.

Tested on Alpine Linux 3.20.5 running kernel 6.6.69.

The compressed blob contains the byte string root::0:0: which patches the 'x' out of the original entry for root (root:x:0:0:root:/root:/bin/sh), bypassing the check for a password in /etc/shadow when su is called.

References:

• Alpine advisory
• Original PoC