359
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or
compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat
FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms
including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary
Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
Effectiveness = Defense in Depth
This is not necessarily a complete solution, since these mechanisms only detect certain types of
overflows. In addition, the result is still a denial of service, since the typical response is to exit the
application.
Phase: Operation
Phase: Build and Compilation
Strategy = Environment Hardening
Run or compile the software using features or extensions that randomly arrange the positions
of a program's executable and libraries in memory. Because this makes the addresses
unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples
include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-
Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their
default memory addresses conflict with other modules, in a process known as "rebasing" (for
Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR
for libraries cannot be used in conjunction with prelink since it would require relocating the
libraries at run-time, defeating the whole purpose of prelinking. For more information on these
techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
Effectiveness = Defense in Depth
These techniques do not provide a complete solution. For instance, exploits frequently use a bug
that discloses memory addresses in order to maximize reliability of code execution [REF-1337]. It
has also been shown that a side-channel attack can bypass ASLR [REF-1333]
Phase: Operation
Strategy = Environment Hardening
Use a CPU and operating system that offers Data Execution Protection (using hardware NX
or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX
[REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a
memory address that is part of the code segment. For more information on these techniques see
D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].
Effectiveness = Defense in Depth
This is not a complete solution, since buffer overflows could be used to overwrite nearby
variables to modify the software's state in dangerous ways. In addition, it cannot be used in
cases in which self-modifying code is required. Finally, an attack could still cause a denial of
service, since the typical response is to exit the application.
Phase: Implementation
Strategy = Compilation or Build Hardening
Examine compiler warnings closely and eliminate problems with potential security implications,
such as signed / unsigned mismatch in memory operations, or use of uninitialized variables.
Even if the weakness is rarely exploitable, a single failure may lead to the compromise of the
entire system.
Phase: Architecture and Design
Phase: Operation
Strategy = Environment Hardening
CWE Version 4.14
CWE-131: Incorrect Calculation of Buffer Size
CWE-131: Incorrect Calculation of Buffer Size