WhiteWinterWolf Practical IT security, *nix systems & networking

Latest articles in ‘Vulnerability’

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   • php-webshell
   • offsec
   • vulnerability
   • webapp
   • php

   wwwolf’s PHP webshell user’s guide

   Web shells are backdoors relying on server-side scripting languages to be executed by the targeted server and usually accessed through a browser. While focused on wwwolf’s PHP webshell features, some part of this post are general and can be applied to other other webshells as well.

   While some web shells attempt to provide the most complete post-exploitation frameworkas possible, and are therefore heavy and prone to bugs and incompatibilities, wwwolf’s PHP webshell considers the web shell as a transitional step in taking over a server.

   wwwolf’s PHP webshell focuses on the functionalities necessary to do:

   • Local enumeration to discover the target’s environment and choose your next step.
   • Payloads and toolkits files transfer and execution, to proceed with your next step.

   It tries its best to:

   • Be unobtrusive, with a simple yet efficient interface.
   • Be reliable, being as tolerant as possible regarding the target’s environment and …

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    • offsec
    • vulnerability
    • drupal
    • webapp
    • php
    • sql

    Drupageddon revisited: a new path from SQL injection to remote command execution (CVE-2014-3704)

    Usually Drupal teams do a great job into ensuring a reasonable security level to their users. Most of the Drupal critical vulnerabilities come from community modules, modules which are hosted on a central place where the ones not conforming with Drupal security requirement get a specific red banner (“This module is unsupported due to a security issue the maintainer didn’t fix.”) and are tagged as abandoned.

    However, mistakes still happen, as Stefan Horst discovered in 2014 when he found out the Drupageddon vulnerability, also known as CVE-2014-3704 and Drupal SA-CORE-2014-005.

    I find this vulnerability quite interesting as it is an SQL injection vulnerability affecting Drupal core which relies on PDO for its database accesses which, in theory, should make it immune to such vulnerability.

    Moreover, we will see that Drupal’s features allow to extend this vulnerability way further than a simple SQL injection. We will …

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    • lab
    • offsec
    • vulnerability
    • networking
    • cisco

    DHCP exploitation guide

    DHCP allows devices to automatically get their network configuration when bringing up a network interface (typically when booting).

    This configuration usually includes, among other thing, the IP address attributed to the device, the DNS domain name and the IP address of the default router, of the DNS server and of the NetBIOS name server.

    This configuration, is allocated to the device only for a given time: the lease time. Lease time may vary largely depending on the environment requirements. It is typical to find values ranging from a few dozen of minutes to a few weeks. When half of the lease time expired, the device starts to try get in touch with the DHCP server to renew the lease.

    Clients initially asking for the attribution of an IP address start by broadcasting a DHCP DISCOVER message.

    A typical DHCP exchange is as follow:

    

    1. DISCOVER: The client without IP address configured …

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    • lab
    • offsec
    • vulnerability
    • networking
    • cisco
    • macof.py

    MAC address table overflow

    The main practical difference between a legacy hub and a switch is that the switch will do its best to forward ethernet frames only on the port allowing to reach the recipient, it won’t blindly forward everything everywhere as as a dumb hub would do.

    To achieve this, upon reception of a frame the switch stores the senders MAC address associated to its input port in an internal memory, usually implemented as a CAM table. Thanks to this information, would a packet have the same address as recipient, the switch will now forward this packet only to this port and not the other ones.

    I already wrote a more focused article on MAC table overflow within the context of GNS3 simulated environments, which resulted in patch being submitted upstream and initiated the development of the macof.py tool. The original article is available here.

    In this article I detailed …

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    • lab
    • offsec
    • vulnerability
    • networking
    • cisco

    Spanning Tree Protocol exploitation

    As we saw in the previous post, Wireshark revealed us the presence of STP messages.

    The Spanning Tree Protocol is used to detect topology loops and build the most efficient forwarding path between interconnected switches. Topology loops are not a mistake but a way to add redundancy to a topology. Would a link break, the STP protocol detects it and recalculate a new most efficient tree.

    In sane networks, access ports should not deliver STP messages to end-devices, but this is not the default and, as Wireshark told us, not the case in our lab. This lets the attacker the possibility to simulate a topology change by sending maliciously crafted STP messages.

    For this lab we will need at least the User_1 and Server_1 devices to be available:

    

    Warning

    The support of STP in the IOU images I tested was very buggy, STP port state was ignored and frames systematically …

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    • lab
    • offsec
    • vulnerability
    • networking
    • cisco

    Practical network layer 2 exploitation: passive reconnaissance

    This post is part of a series about practical network layer 2 exploitation.

    Now is the time to change your network administrator hat for the attacker one. Your own, known network now becomes an unfamiliar target.

    Before rushing and banging against the nearest devices, it may wiser to just stand back and listen.

    On switched networks, users are somewhat isolated from each other thanks to the separation of collision domains. All that remain is some kind white noise… but this white noise in itself can bring invaluable information to an attacker!

    In particular we will see how, simply by passively listening to this white noise, an attacker will be able to detect several weaknesses affecting the network and plan his next steps.

    In this lab no interaction will occur with either the Admins or the Servers VLANs, the User_1 workstation will be required only for the DHCP Discover messages part …

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    • lab
    • offsec
    • vulnerability
    • networking
    • cisco

    Practical network layer 2 exploitation: introduction

    This post initiates a series demonstrating network layer 2 exploitation and protection techniques from practical point-of-view.

    This series will rely on the following topology (click to enlarge):

    

    This topology is composed of three VLANs:

    • Users (VLAN 1) and Admins (VLAN 2) both contain end-user workstations, they are isolated from each other.
    • Both can access machines located in Servers (VLAN 3).

    The attacker is connected to the Users VLAN.

    In this series we will see how the attacker can leverage various layer 2 configuration weaknesses to disrupt the network, hop from one VLAN to another, and intercept users communication, independently of their location in the topology.

    We will limit ourselves to basic techniques as an attempt to demonstrate that pwning a insufficiently secured network doesn’t involve any high technology or knowledge. When appropriate we will also see how the attacks can be generalized to other real-life scenarios.

    Creating the topology …

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    • freebsd
    • *nix
    • offsec
    • vulnerability

    FreeBSD jail SHM hole (CVE-2017-1087)

    In FreeBSD early days, shared memory (SHM) objects were associated to an actual file system object. Each jail having its own filesystem root, SHM object were therefore not reachable by other jails.

    FreeBSD 7.0 switched to a purely abstract representation of SHM objects. They are now just names, with no relation to the underlying filesystem.

    Due to this, any jail gained a read-write access to any SHM object system-wide, with no available workaround to prevent or limit this (this is not to be confused with IPCs which can be disabled on a per-jail basis, here there is strictly no way to prevent the issue).

    This issue has been published in the FreeBSD Security Advisory FreeBSD-SA-17:09 and CVE-2017-1087.

    Proof-of-concept

    fbsd-shm-hole.c is a small POC allowing to quickly test and demonstrate the issue.

    Download
    SHA-512 OpenPGP

    1. Compile and copy this tool in two different jails …

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