This attack attempts to trigger and exploit a deadlock condition in the
target software to cause a denial of service. A deadlock can occur when two
or more competing actions are waiting for each other to finish, and thus
neither ever does. Deadlock condition are not easy to detect.
Attack Execution Flow
The attacker initiates an exploratory phase to get
familiar with the system.
The attacker triggers a first action (such as
holding a resource) and initiates a second action
which will wait for the first one to finish.
If the target program has a deadlock condition,
the program waits indefinitevely resulting in a
denial of service.
Attack Prerequisites
The target host has a deadlock condition. There are four conditions for a
deadlock to occur, known as the Coffman conditions (See reference,
Wikipedia)
The target host exposes an API to the user.
Typical Likelihood of Exploit
Likelihood: Low
Methods of Attack
Analysis
API Abuse
Examples-Instances
Description
An example of a deadlock which may occur in database products is the
following. Client applications using the database may require exclusive
access to a table, and in order to gain exclusive access they ask for a
lock. If one client application holds a lock on a table and attempts to
obtain the lock on a second table that is already held by a second
client application, this may lead to deadlock if the second application
then attempts to obtain the lock that is held by the first application
(Source: Wikipedia, http://en.wikipedia.org/wiki/Deadlock)
Attacker Skills or Knowledge Required
Skill or Knowledge Level: Medium
This type of attack may be sophisticated and require knowledge about
the system's resources and APIs.
Probing Techniques
Description
The attacker can probe by trying to hold resources and call APIs which
are directly using the same resources.
Description
The attacker may try to find actions (threads, processes) competing
for the same resources.
Solutions and Mitigations
Use known algorithm to avoid deadlock condition (for instance non-blocking
synchronization algorithms).
For competing actions use well known libraries which implement
synchronization.
Description
