This specific weakness is impossible to detect using black box methods. While an analyst could examine memory to see that it has not been scrubbed, an analysis of the executable would not be successful. This is because the compiler has already removed the relevant code. Only the source code shows whether the programmer intended to clear the memory or not, so this weakness is indistinguishable from others.
CWE-733 Base Incomplete
Compiler Optimization Removal or Modification of Security-critical Code
This vulnerability occurs when a compiler's optimization process unintentionally strips out or alters security-critical code that a developer intentionally wrote, leaving the application exposed.
Definition
What is CWE-733?
This vulnerability occurs when a compiler's optimization process unintentionally strips out or alters security-critical code that a developer intentionally wrote, leaving the application exposed.
Developers often add specific checks, like verifying a buffer size or clearing sensitive data from memory, as a deliberate security measure. However, when the code is compiled with high optimization levels (like -O2 or -O3), the compiler might analyze this security code and deem it 'unnecessary' for the program's core functionality. In an effort to make the software faster or smaller, the compiler removes or modifies these crucial safeguards, effectively creating a hidden vulnerability that wasn't present in the source code.
This issue is particularly dangerous because the vulnerability is invisible in the source code review. It only manifests in the compiled binary, making it a silent failure. To mitigate this, developers must be aware of compiler-specific behaviors, use volatile qualifiers or compiler barriers (like `asm volatile("" ::: "memory")` in GCC) for critical operations, and test security-sensitive code with optimization enabled to ensure protections remain intact after compilation.
Real-world impact
Real-world CVEs caused by CWE-733
-
C compiler optimization, as allowed by specifications, removes code that is used to perform checks to detect integer overflows.
-
Chain: compiler optimization (CWE-733) removes or modifies code used to detect integer overflow (CWE-190), allowing out-of-bounds write (CWE-787).
How attackers exploit it
Step-by-step attacker path
- 1
The following code reads a password from the user, uses the password to connect to a back-end mainframe and then attempts to scrub the password from memory using memset().
- 2
The code in the example will behave correctly if it is executed verbatim, but if the code is compiled using an optimizing compiler, such as Microsoft Visual C++ .NET or GCC 3.x, then the call to memset() will be removed as a dead store because the buffer pwd is not used after its value is overwritten [18]. Because the buffer pwd contains a sensitive value, the application may be vulnerable to attack if the data are left memory resident. If attackers are able to access the correct region of memory, they may use the recovered password to gain control of the system.
- 3
It is common practice to overwrite sensitive data manipulated in memory, such as passwords or cryptographic keys, in order to prevent attackers from learning system secrets. However, with the advent of optimizing compilers, programs do not always behave as their source code alone would suggest. In the example, the compiler interprets the call to memset() as dead code because the memory being written to is not subsequently used, despite the fact that there is clearly a security motivation for the operation to occur. The problem here is that many compilers, and in fact many programming languages, do not take this and other security concerns into consideration in their efforts to improve efficiency.
- 4
Attackers typically exploit this type of vulnerability by using a core dump or runtime mechanism to access the memory used by a particular application and recover the secret information. Once an attacker has access to the secret information, it is relatively straightforward to further exploit the system and possibly compromise other resources with which the application interacts.
Vulnerable code example
Vulnerable C
The following code reads a password from the user, uses the password to connect to a back-end mainframe and then attempts to scrub the password from memory using memset().
void GetData(char *MFAddr) {
char pwd[64];
if (GetPasswordFromUser(pwd, sizeof(pwd))) {
if (ConnectToMainframe(MFAddr, pwd)) {
```
// Interaction with mainframe*
}}
memset(pwd, 0, sizeof(pwd));} Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-733
- Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
- Implementation Validate input at trust boundaries; use allowlists, not denylists.
- Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
- Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
- Operation Monitor logs for the runtime signals listed in the next section.
Detection signals
How to detect CWE-733
This weakness is only detectable using white box methods (see black box detection factor). Careful analysis is required to determine if the code is likely to be removed by the compiler.
Plexicus auto-detects CWE-733 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-733?
How serious is CWE-733?
What languages or platforms are affected by CWE-733?
How can I prevent CWE-733?
How does Plexicus detect and fix CWE-733?
Where can I learn more about CWE-733?
Frequently asked questions
What is CWE-733?
This vulnerability occurs when a compiler's optimization process unintentionally strips out or alters security-critical code that a developer intentionally wrote, leaving the application exposed.
How serious is CWE-733?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-733?
MITRE lists the following affected platforms: C, C++, Compiled.
How can I prevent CWE-733?
Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.
How does Plexicus detect and fix CWE-733?
Plexicus's SAST engine matches the data-flow signature for CWE-733 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-733?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/733.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-733
CWE-1038 Parent
Insecure Automated Optimizations
This vulnerability occurs when software uses automated tools to optimize code for performance or efficiency, but those optimizations…
CWE-1037 Sibling
Processor Optimization Removal or Modification of Security-critical Code
This vulnerability occurs when a processor's performance optimization unintentionally strips out or alters security-critical code that a…
CWE-14 Child
Compiler Removal of Code to Clear Buffers
A compiler optimization can remove security-critical code intended to wipe sensitive data from memory, leaving secrets exposed. This…
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