Any condition where the attacker has the ability to write an arbitrary value to an arbitrary location, often as the result of a buffer overflow.
Consequences
- Access control (memory and instruction processing): Clearly, write-what-where conditions can be used to write data to areas of memory outside the scope of a policy. Also, they almost invariably can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy.
- Availability: Many memory accesses can lead to program termination, such as when writing to addresses that are invalid for the current process.
- Other: When the consequence is arbitrary code execution, this can often be used to subvert any other security service.
Exposure period
- Requirements: At this stage, one could specify an environment that abstracts memory access, instead of providing a single, flat address space.
- Design: Many write-what-where problems are buffer overflows, and mitigating technologies for this subset of problems can be chosen at this time.
- Implementation: Any number of simple implementation flaws may result in a write-what-where condition.
Platform
- Languages: C, C++, Fortran, Assembly
- Operating platforms: All, although partial preventative measures may be deployed depending on environment.
Required resources
Any
Severity
Very High
Likelihood of exploit
High
When the attacker has the ability to write arbitrary data to an arbitrary location in memory, the consequences are often arbitrary code execution. If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), he can redirect a function pointer to his own malicious code.
Even when the attacker can only modify a single byte using a write-what-where problem, arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data - such as a flag indicating whether the user is an administrator.