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                            CERT-Renater

                Note d'Information No. 2026/VULN105
_____________________________________________________________________

DATE                : 02/02/2026

HARDWARE PLATFORM(S): /

OPERATING SYSTEM(S): Systems running PsySH versions prior to 0.12.19, 
                                         0.11.23.

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https://github.com/bobthecow/psysh/security/advisories/GHSA-4486-gxhx-5mg7
_____________________________________________________________________

Local Privilege Escalation via CWD .psysh.php auto-load
Moderate
bobthecow published GHSA-4486-gxhx-5mg7 Jan 30, 2026

Package
psy/psysh (Composer)

Affected versions
>= 0.12.0, <= 0.12.18
<= 0.11.22

Patched versions
0.12.19
0.11.23


Description

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.php in 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.


Severity
Moderate
6.7/ 10

CVSS v3 base metrics
Attack vector
Local
Attack complexity
High
Privileges required
Low
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

CVE ID
CVE-2026-25129

Weaknesses
Weakness CWE-427

Credits

    @aqhmal aqhmal Reporter


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