New Hack Exploits Common Programming Error

buzzardsbay writes "TechTarget's security editor, Dennis Fisher is reporting that researchers at Watchfire Inc. have discovered a reliable method for exploiting a common programming error, which until now had been considered simply a quality problem and not a security vulnerability. According to the article, the researchers stumbled upon the method for remotely exploiting dangling pointers by chance while they were running the company's AppScan software against a Web server. The good folks at Watchfire will detail the technique in a presentation at the Black Hat Briefings in Las Vegas in August, Fisher writes."

Comments

Known since 2005

[drspliff]

"When Watchfire first alerted Microsoft's security response team to what Afek and Sharabani had found, they were met with skepticism, and understandably so, Allan said. The company had known since 2005 about the IIS bug that caused the crash, but it was considered a simple denial-of-service problem and not remotely exploitable."

Worded a little ambiguously, but I presume it's Microsoft their talking about... How can a bug like this get through the QA process since 2005 and multiple product versions without getting fixed?

Re:Pleasantly surprised!

[Wavicle]

Yes and no. The pointer in question may have a lifetime greater than that of the object being pointed to. Example:


void (*myFuncPtr)() = NULL;

void cleanUp() {
    item listItem = firstItem;

    while ( listItem != NULL ) {

        myFuncPtr = listItem->fcn;
        myFuncPtr();

        tempItem = listItem->next;
        free(listItem);
        listItem = tempItem;
    }
} // myFuncPtr is now dangling!


A little contrived, sure, but it is an example of how a pointer might get left dangling.

- It doesn't have to be a function pointer.

[DogFacedJo]

In OO languages a pointer to an object works almost as well. The object pointed to in many implementations begins with a type field. This is usually a pointer to the class's virtual function table - usually implemented as a table of function pointers.
    That is to say - if the object is referenced through a bad pointer, *and executes* any methods of that object's type - then it could be used to run someone elses code. They'll need to have filled some memory with something that can be interpreted as a virtual function table that points at something that can be interpreted as code. Which is doable.
    If the processor/OS has set an app to able to write to it's executable memory, then it is vulnerable to this class of vulnerability.
    Many OS's and C++, Objective C and *java* implementations default to this.

Pascal and perl used (maybe they still do) stubby things that required that the *stack* be executable, nevermind just data... *buffer overruns* are much easier when the stack is executable.

    Java is interesting. Modern VMs do a lot of dynamic optimization - this means that they write on code that is actually running. They need OS permission to do so (in decent OSs?) so now you *have* to give the VM's process that permission in order to run Java. Now any dangling pointers in the VM implemention are potentially exploitable. Or if the memory manager has a bug and improperly deallocates an object... Or if the application has to call a library and that library accidentally accesses a reference to an object that was already released by java. Or maybe the app calls the OS - and the OS has a dangling pointer (say to a data structure that the Java VM needed to allocate). If you can fill the Java heap with executable exploit data, then if someone, anyone, jumps into it - they are toast.

  I hope this helps. There is likely an actual paper that they will present. It will document one or several of the myriad ways to exploit dangling pointers - hopefully more efficiently than previously.