1705
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: Implementation
Consider adhering to the following rules when allocating and managing an application's memory:
Double check that the buffer is as large as specified. When using functions that accept a number
of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the
source buffer size, it may not NULL-terminate the string. Check buffer boundaries if accessing
the buffer in a loop and make sure there is no danger of writing past the allocated space. If
necessary, truncate all input strings to a reasonable length before passing them to the copy and
concatenation functions.
Phase: Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are
duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side
checks by modifying values after the checks have been performed, or by changing the client to
remove the client-side checks entirely. Then, these modified values would be submitted to the
server.
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
CWE Version 4.14
CWE-805: Buffer Access with Incorrect Length Value
CWE-805: Buffer Access with Incorrect Length Value