The product does not properly synchronize shared data, such as
static variables across threads, which can lead to undefined behavior and
unpredictable data changes.
Time of Introduction
Architecture and Design
Implementation
Applicable Platforms
Languages
All
Demonstrative Examples
Example 1
Java
public static class Counter extends HttpServlet {
static int count = 0;
protected void doGet(HttpServletRequest in,
HttpServletResponse out)
throws ServletException, IOException {
out.setContentType("text/plain");
PrintWriter p = out.getWriter();
count++;
p.println(count + " hits so far!");
}
}
Potential Mitigations
Phase
Description
A shared variable vulnerability can be prevented by removing the use
of static variables used between servlets or to provide protection when
shared access is absolutely needed. In this case, access should be
synchronized.
Other Notes
The vulnerability can exist in servlets because a servlet is
multi-threaded, and shared static variables are not protected from
concurrent access. This is a typical programming mistake in J2EE
applications, since the multi-threading is handled by the framework. The use
of shared variables can be exploited by attackers to gain information or to
cause denial of service conditions. If this shared data contains sensitive
information, it may be manipulated or displayed in another user session. If
this data is used to control the application, its value can be manipulated
to cause the application to crash or perform poorly.
Description
