A guided tour to someone else's network
Email-Based Attacks
So what happens if you hit a dead end and can't find any vulnerable services to attack? What if the network is properly segmented and there is no path from the web server you have compromised to the internal network? Go with email. Because virtually all email clients now handle HTML, multimedia content, and so on, they rely on the underlying system libraries to parse this content.
The bad news is that virtually every HTML rendering engine (WebKit, Gecko, Microsoft HTML Rendering Engine, Microsoft Word, etc.) has exploitable flaws, and most image and multimedia files also have exploitable flaws. If you can sneak a malicious email past the scanners, you can probably cause code execution on the victim's machine.
To make things even easier, you also have the option of attaching a file that targets any number of local programs, currently the more popular ones are Adobe Reader (with many JBIG2-related vulnerabilities), Open Office, and of course, Microsoft Office.
But don't all sites have virus scanning of incoming email and blocking of executable attachments? Well, this is where the information harvested about the target really comes in handy. If you can find a list of the executives, or a company phone directory (which will sometimes even lists the department someone is in), you can craft email messages that look something like the message shown in Figure 6.
Creating Malicious PDF Files
The only reason I am picking on PDFs and not some other file format (such as TIFF, AVI, DOC, and ODT) is that, in the last few months, a lot of easy-to-use tools and exploits for Adobe Reader have been released, and Reader is one of the few applications that is almost guaranteed to be on a system. (If it isn't there, the system probably has an equally vulnerable program, such as Foxit). Oh, and you can embed JavaScript into PDF files (Figure 7) that is executed by default, although you can disable JavaScript support in Acrobat Reader [18].
Didier Stevens has released a tool called make-pdf-javascript.py that allows you to embed arbitrary JavaScript into a PDF file [19]. Fortunately, this tool doesn't do any obfuscation or other tricks to hide the JavaScript, although other tools do. However, I will leave finding them as an exercise for the reader).
One note: You might have to run the script through dos2unix to fix the line breaks, and depending on your version of Python, there is a finally: clause in line 63 that you might need to remove. Just be sure to remove one tab from the line that follows as well and it will run fine.
Bringing It All Together for the Win
Individually, most of these attacks won't get you very far. You might gain access to a web application, read someone's email, or view a file on the server. But by combining techniques, such as writing arbitrary contents to a file and then including that file so that the PHP code within it is executed (Figure 8), an attacker can launch local attacks, of which there are plenty. In the first half of 2009 alone, the Linux kernel has suffered because of several locally exploitable vulnerabilities (ptrace_attach, udev, netlink, and exit_notify) for which exploit code exists publicly (just search Milw0rm for "Linux Kernel").
Exploiting a system via the kernel is particularly effective because a) you know it's installed and b) upgrading a Linux kernel on many web hosts is either a complete pain or simply not possible. Once attackers have the ability to exploit code locally, it's only a matter of time before they can execute code as the root user.
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you've found an article to be beneficial.
News
-
Linux Kernel Reducing Long-Term Support
LTS support for the Linux kernel is about to undergo some serious changes that will have a considerable impact on the future.
-
Fedora 39 Beta is Now Available for Testing
For fans and users of Fedora Linux, the first beta of release 39 is now available, which is a minor upgrade but does include GNOME 45.
-
Fedora Linux 40 to Drop X11 for KDE Plasma
When Fedora 40 arrives in 2024, there will be a few big changes coming, especially for the KDE Plasma option.
-
Real-Time Ubuntu Available in AWS Marketplace
Anyone looking for a Linux distribution for real-time processing could do a whole lot worse than Real-Time Ubuntu.
-
KSMBD Finally Reaches a Stable State
For those who've been looking forward to the first release of KSMBD, after two years it's no longer considered experimental.
-
Nitrux 3.0.0 Has Been Released
The latest version of Nitrux brings plenty of innovation and fresh apps to the table.
-
Linux From Scratch 12.0 Now Available
If you're looking to roll your own Linux distribution, the latest version of Linux From Scratch is now available with plenty of updates.
-
Linux Kernel 6.5 Has Been Released
The newest Linux kernel, version 6.5, now includes initial support for two very exciting features.
-
UbuntuDDE 23.04 Now Available
A new version of the UbuntuDDE remix has finally arrived with all the updates from the Deepin desktop and everything that comes with the Ubuntu 23.04 base.
-
Star Labs Reveals a New Surface-Like Linux Tablet
If you've ever wanted a tablet that rivals the MS Surface, you're in luck as Star Labs has created such a device.