Definition
Validates that a referenced exception handler pointer is a valid exception handler.
How It Works
When a process encounters an exception, it calls an exception handler to deal with the exception. The method by which this exception handler is determined varies by the operating system. The exception handler is called, even if it is the default exception handler to terminate the program and display a message that the program stopped working. In the case that no valid exception handler is found, the program would fail to proceed as normal and could be programmed to terminate.
In Windows, the address of the exception registration record is stored at the very start of the Thread Information Block; the GS register points to this structure.
The exception registration record contains two pointers: a pointer to the next exception registration record should this handler fail to handle the exception, and a pointer to the handler.
A buffer overflow can overwrite the saved return pointer with an invalid location to execute memory; this often triggers the exception handler chain, which could also be corrupted by the buffer overflow. Although Process Exception Handler Validation does not make sure that the exception handler pointer or the code at the exception handler was unaltered, or that the exception handler code is secure, this technique does ensure that the pointer is at least an exception handler that could be called by the program.
With Process Exception Handler Validation, before the handler is called, it checks the exception handler against a source of valid exception handlers. If the requested handler is not in this list, other techniques such as those in Process Eviction might be invoked, such as Process Termination to end the current process, or Executable Blacklisting to blacklist the potentially vulnerable or malfunctioning executable.
Runtime valid exception handler source generation
The source of valid exception handlers could be generated at runtime, with the risk of the information that is used to determine the validity of exception handlers being compromised.
Compile-time
The source of valid exception handlers could also be generated at compile time or as a binary patch. Given the source code, it would be rather straightforward to find the exceptions, as they are pointed in the catch statement of a try-catch clause and the compiler must already generate the code to call exceptions from this.
Considerations
If the program file can be altered by the attacker, then the security could be bypassed by replacing it with any desired program, without even bypassing SEH.
If the attacker was already able to overwrite the code for a valid exception handler via other functionality in the program, this defense would not prevent arbitrary code execution. If an exception handler recognized as valid is vulnerable, it would be executed anyway.
SafeSEH might be applied only to some executable files or modules, allowing an attacker to call any piece of code as an exception handler in the unprotected modules.
Implementation perspective
Exception Handler Pointer Validation should be treated as a technical defensive capability rather than a product checkbox. In practice, teams should define the protected scope, the conditions under which the technique acts, and the observable evidence that demonstrates the intended behavior. For this technique, likely engineering context includes the relevant system, activity, and evidence sources.
Use the technique to increase the effort, prerequisites, or constraints an adversary must overcome before exploitation or misuse succeeds.
Questions to ask
- Which component, configuration, credential, interface, or behavior is being hardened?
- What secure baseline or policy defines the intended state?
- How are exceptions approved, time-limited, and reviewed?
- How is the hardened state verified after deployment and significant change?
Evidence and validation
- Approved hardening standards and configuration baselines
- Automated configuration or integrity assessment results
- Exception records with owners, rationale, and expiration dates
- Test results demonstrating that the intended restriction is enforced
Common failure patterns
- A secure setting is documented but not enforced consistently across the environment.
- Hardening breaks required functions and is permanently weakened through undocumented exceptions.
- Teams measure deployment of a product rather than verification of the hardened condition.
This implementation perspective is original Bare Metal Cyber educational content. It does not replace the official D3FEND definition or establish that a specific product implements the technique.
Technique hierarchy
Top-level family
Parent techniques
Direct child techniques
None listed at this level.
Artifacts and ontology entities
These relationships describe how D3FEND connects a defensive technique to artifacts or other ontology entities. They describe graph semantics, not a product certification.
Explicit technique relationships
ATT&CK Enterprise mitigation relationships
These links come from the D3FEND ontology’s ATT&CK mitigation mapping. They help users navigate between the knowledge bases and do not guarantee mitigation effectiveness.
Authoritative sources
- Open this technique on the official D3FEND website ↗
- Open the official ontology resources ↗
- /SAFESEH (Image has Safe Exception Handlers) ↗Microsoft · Mike Blome, Saisang Cai, Colin Robertson, Mike Jones, NextTurn, Gordon Hogenson · UserManualReference
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