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GHSA-4486-gxhx-5mg7
No affected components available
Summary
PsySH automatically loads and executes a .psysh.php file from the Current Working Directory (CWD) on startup. If an attacker can write to a directory that a victim later uses as their CWD when launching PsySH, the attacker can trigger arbitrary code execution in the victim's context. When the victim runs PsySH with elevated privileges (e.g., root), this results in local privilege escalation.
Details
PsySH supports per-directory configuration via a .psysh.php file located in the process CWD. This file is executed implicitly when PsySH starts, without requiring explicit opt-in and without validating that the file and directory are safe (e.g., owned by the current user and not group/world-writable).
This enables a CWD poisoning scenario: a low-privileged user can plant a malicious .psysh.php in any directory they can write to, then wait for a higher-privileged user to start PsySH while their shell is in that directory.
PoC
- As a low-privileged user, create a malicious
.psysh.phpin an attacker-writable directory (example:/tmp):
bob@localhost:/tmp$ echo "<?php system('id > poc.txt'); ?>" > .psysh.php
bob@localhost:/tmp# ls -lah .psysh.php
-rw-r--r-- 1 bob bob 33 Jan 28 11:17 .psysh.php
- As the victim user, start PsySH with CWD set to that directory and exit:
root@localhost:/tmp# cd /tmp
root@localhost:/tmp# ./psysh
Psy Shell v0.12.18 (PHP 8.1.2-1ubuntu2.23 — cli) by Justin Hileman
New PHP manual is available (latest: 3.0.1). Update with `doc --update-manual`
> exit
INFO Goodbye.
- Verify code execution triggered in the victim context:
bob@localhost:/tmp$ ls -lah poc.txt
-rw-r--r-- 1 root root 39 Jan 28 11:19 poc.txt
bob@localhost:/tmp$ cat poc.txt
uid=0(root) gid=0(root) groups=0(root)
Impact
This is a CWD configuration poisoning issue leading to arbitrary code execution in the victim user’s context. If a privileged user (e.g., root, a CI runner, or an ops/debug account) launches PsySH with CWD set to an attacker-writable directory containing a malicious .psysh.php, the attacker can execute commands with that privileged user’s permissions, resulting in local privilege escalation.
Downstream consumers that embed PsySH inherit this risk. For example, Laravel Tinker (php artisan tinker) uses PsySH. If a privileged user runs Tinker while their shell is in an attacker-writable directory, the .psysh.php auto-load behavior can be abused in the same way to execute attacker-controlled code under the victim’s privileges.
The vulnerability requires local access to the device to be exploited. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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