Message-ID: <C56B81159AD346478B2C9D1487742F0B467928A2@portcullis-security.com>
Date: Thu, 29 Oct 2015 10:27:06 +0000
From: Portcullis Advisories <advisories@...tcullis-security.com>
To: "'vuln@...unia.com'" <vuln@...unia.com>, "'moderators@...db.org'"
 <moderators@...db.org>, "'fulldisclosure@...lists.org'"
 <fulldisclosure@...lists.org>, "'bugtraq@...urityfocus.com'"
 <bugtraq@...urityfocus.com>
Subject: [FD] CVE-2015-7724 - Privilege Escalation Via Symlink Attacks On
 POSIX Shared Memory With Insecure Permissions In AMD fglrx-driver

Vulnerability title: Privilege Escalation Via Symlink Attacks On POSIX Shared Memory With Insecure Permissions In AMD fglrx-driver
CVE: CVE-2015-7724
Vendor: AMD
Product: fglrx-driver
Affected version: 15.7
Fixed version: 15.9
Reported by: Tim Brown
Details:

In the process of validating the fix for CVE-2015-7723, it has been identified that the userland portion of the fglrx-driver utilised by Xorg still allows privilege escalation via symlink attacks on POSIX shared memory with insecure permissions.

As with the original vulnerability, with a Linux kernel where fs.protected_symlinks is not set to 1, or where this feature is not available, the following code (present in shared libraries distributed as part of fglrx-driver) calls shm_open() with insecure flags specified which allows the Linux kernel to follow an existent symlink under /dev/shm:

mov $0x1b6,%edx ; $edx (mode) = 0666
mov $0x42,%esi ; $esi (oflag) = O_CREAT | O_RDWR - missing O_EXCL
mov %r13,%rdi
callq 208b68 <shm_open@plt>

The same call to shm_open() requests that the permissions of newly created file are 0666 and as a result, an arbitrary file, owned by root, with permissions of 0666 can be created anywhere on the filesystem

Furthermore, the code then proceeds to force the permissions on the resultant file to 0666 using fchmod(). This can be useful if the symlink target already exists:

mov $0x1b6,%esi ; $esi (mode) = 0666
mov %eax,%edi
callq 209058 <fchmod@plt>

Further details at:

https://www.portcullis-security.com/security-research-and-downloads/security-advisories/cve-2015-7724/

Copyright:
Copyright (c) Portcullis Computer Security Limited 2015, All rights reserved worldwide. Permission is hereby granted for the electronic redistribution of this information. It is not to be edited or altered in any way without the express written consent of Portcullis Computer Security Limited.

Disclaimer:
The information herein contained may change without notice. Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. In no event shall the author/distributor (Portcullis Computer Security Limited) be held liable for any damages whatsoever arising out of or in connection with the use or spread of this information.

###############################################################
This email originates from the systems of Portcullis
Computer Security Limited, a Private limited company, 
registered in England in accordance with the Companies 
Act under number 02763799. The registered office 
address of Portcullis Computer Security Limited is: 
Portcullis House, 2 Century Court, Tolpits Lane, Watford, 
United Kingdom, WD18 9RS.  
The information in this email is confidential and may be 
legally privileged. It is intended solely for the addressee. 
Any opinions expressed are those of the individual and 
do not represent the opinion of the organisation. Access 
to this email by persons other than the intended recipient 
is strictly prohibited.
If you are not the intended recipient, any disclosure, 
copying, distribution or other action taken or omitted to be 
taken in reliance on it, is prohibited and may be unlawful. 
When addressed to our clients any opinions or advice 
contained in this email is subject to the terms and 
conditions expressed in the applicable Portcullis Computer 
Security Limited terms of business.
###############################################################

#####################################################################################
This e-mail message has been scanned for Viruses and Content and cleared 
by MailMarshal.
#####################################################################################

_______________________________________________
Sent through the Full Disclosure mailing list
https://nmap.org/mailman/listinfo/fulldisclosure
Web Archives & RSS: http://seclists.org/fulldisclosure/

Powered by blists - more mailing lists