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Showing posts from 2015

Microsoft .NET MVC ReDoS (Denial of Service) Vulnerability - CVE-2015-2526 (MS15-101)

Microsoft released a security bulletin (MS15-101) describing a .NET MVC Denial of Service vulnerability (CVE-2015-2526) that I reported back in April. This blog post analyses the vulnerability in details, starting from the theory and then providing a PoC exploit against a MVC web application developed with Visual Studio 2013.
For those of you who want to see the bug, you can directly skip to the last part of this post or watch the video directly... ;-)

A bit of theory

The .NET framework (4.5 tested version) uses backtracking regular expression matcher when performing a match against an expression. Backtracking is based on the NFA (non-deterministic finite automata) algorithm engine which is designed to validate all input states. By providing an “evil” regex expression – an expression for which the engine can be forced to calculate an exponential number of states - it is possible to force the engine to calculate an exponential number of states, leading to a condition defined such as “ca…

Pwning a thin client in less than two minutes

Have you ever encountered a zero client or a thin client? It looks something like this...

If yes, keep reading below, if not, then if you encounter one, you know what you can do if you read below...

The model above is a T520, produced by HP - this model and other similar models are typically employed to support a medium/large VDI (Virtual Desktop Infrastructure) enterprise.

These clients run a Linux-based HP ThinPro OS by default and I had a chance to play with image version T6X44017 in particular, which is fun to play with it, since you can get a root shell in a very short time without knowing any password...

Normally, HP ThinPro OS interface is configured in a kiosk mode, as the concept of a thin/zero client is based on using a thick client to connect to another resource. For this purpose, a standard user does not need to authenticate to the thin client per se and would just need to perform a connection - e.g. VMware Horizon View. The user will eventually authenticate through the c…

Playing with Kemp Load Master

Kemp virtual load master is a virtual load-balancer appliance which comes with a web administrative interface. I had a chance to test it and this blog post summarises some of the most interesting vulnerabilities I have discovered and which have not been published yet. For those of you who want to try it as well, you can get a free trial version here: http://kemptechnologies.com/server-load-balancing-appliances/virtual-loadbalancer/vlm-download

By default, Kemp web administrative interface is protected by Basic authentication, so the vulnerabilities discussed in the post below can either be exploited attacking an authenticated user via CSRF or XSS based attacks.

The following vulnerabilities were discovered when looking at Kemp Load Master v.7.1-16 and some of them should be fixed in the latest version (7.1-20b or later).

Change logs of the fixed issues can be found at the following page:

"PD-2183 Functions have been added to sanitize input in the WUI in order toresolve some secur…