Local, automatic variables assume unexpected values if they are read before they are initialized. The The C Standard, 6.7.911, paragraph 1011, specifies [ISO/IEC 9899:20112024]
If an object that has automatic storage duration is not initialized explicitly, its value representation is indeterminate.
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EXP33-C-EX1: Reading uninitialized memory by an lvalue of type unsigned char that could not have been declared with the register storage class does not trigger undefined behavior. The unsigned char type is defined to not have a trap representation, which allows for moving bytes without knowing if they are initialized. (See the C Standard, 6.2.6.1, paragraph 3.) However, ) The requirement that register could not have been used (not merely that it was not used) is because on some architectures, such as the Intel Itanium, registers have a bit to indicate whether or not they have been initialized. The C Standard, 6.3.2.1, paragraph 2, allows such implementations to cause a trap for an object that never had its address taken and is stored in a register if such an object is referred to in any way.
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| Tool | Version | Checker | Description | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Astrée |
| uninitialized-local-read uninitialized-variable-use | Partially Fully checked | ||||||||||||||||||
| Axivion Bauhaus Suite |
| CertC-EXP33 | |||||||||||||||||||
| CodeSonar |
| LANG.MEM.UVAR | Uninitialized variable | ||||||||||||||||||
| Compass/ROSE | Automatically detects Automatically detects simple violations of this rule, although it may return some false positives. It may not catch more complex violations, such as initialization within functions taking uninitialized variables as arguments. It does catch the second noncompliant code example, and can be extended to catch the first as well | ||||||||||||||||||||
| Coverity |
| UNINIT | Implemented | ||||||||||||||||||
| Cppcheck |
| uninitvar | Detects uninitialized variables, uninitialized pointers, uninitialized struct members, and uninitialized array elements (However, if one element is initialized, then cppcheck assumes the array is initialized.) | ||||||||||||||||||
| GCC | 4.3.5 | Can detect some violations of this rule when the | |||||||||||||||||||
| Cppcheck Premium |
| Klocwork | | Include Page |
| UNINIT.HEAP.MIGHT | LDRA tool suite | |||||||||||||||
| Include Page | LDRA_V | LDRA_V | 53 D, 69 D, 631 S, 652 S | Fully implemented | |||||||||||||||||
| Parasoft C/C++test | 9.5 | BD-BP-NOTINIT | Fully implemented | ||||||||||||||||||
| Parasoft Insure++ | Runtime analysis | ||||||||||||||||||||
| Polyspace Bug Finder | R2016a | Pointer not initialized before dereference Variable not initialized before use | PRQA QA-C | ||||||||||||||||||
| Include Page | PRQA QA-C_v | PRQA QA-C_v | 2961, 2962, 2963, 2966, 2967, 2968, 2971, 2972, 2973, 2976, 2977, 2978 | Fully implemented | PRQA QA-C++ | ||||||||||||||||
| Include Page | cplusplus:PRQA QA-C++_V | cplusplus:PRQA QA-C++_V | 2961, 2962, 2963, 2966, 2967, 2968, 2971, 2972, 2973, 2976, 2977, 2978 | ||||||||||||||||||
| Splint | 3.1.1 | ||||||||||||||||||||
| RuleChecker | |||||||||||||||||||||
| Include Page | RuleChecker_V | RuleChecker_V | uninitialized-local-read uninitialized-variable-use | Partially checked |
Related Vulnerabilities
| uninitvar uninitdata uninitstring uninitMemberVar uninitStructMember | Detects uninitialized variables, uninitialized pointers, uninitialized struct members, and uninitialized array elements (However, if one element is initialized, then cppcheck assumes the array is initialized.) There are FN compared to some other tools because Cppcheck tries to avoid FP in impossible paths. | ||||||||
| GCC | 4.3.5 | Can detect some violations of this rule when the | |||||||
| Helix QAC |
| DF2726, DF2727, DF2728, DF2961, DF2962, DF2963, DF2966, DF2967, DF2968, DF2971, DF2972, DF2973, DF2976, DF2977, DF2978 | Fully implemented | ||||||
| Klocwork |
| UNINIT.HEAP.MIGHT | Fully implemented | ||||||
| LDRA tool suite |
| 53 D, 69 D, 631 S, 652 S | Fully implemented | ||||||
| Parasoft C/C++test |
| CERT_C-EXP33-a | Avoid use before initialization | ||||||
| Parasoft Insure++ |
| Runtime analysis | |||||||
| PC-lint Plus |
| 530, 603, 644, 901 | Fully supported | ||||||
| Polyspace Bug Finder |
| Checks for:
Rule partially covered | |||||||
| PVS-Studio |
| V573, V614, V670, V679, V1050 | |||||||
| RuleChecker |
| uninitialized-local-read | Partially checked | ||||||
| Splint | 3.1.1 | ||||||||
| TrustInSoft Analyzer |
| initialisation | Exhaustively verified (see one compliant and one non-compliant example). |
Related Vulnerabilities
CVE-2009-1888 results from a violation of this rule. Some versions of SAMBA (up to 3.3.5) call a function that takes in two potentially uninitialized variables involving access rights. An CVE-2009-1888 results from a violation of this rule. Some versions of SAMBA (up to 3.3.5) call a function that takes in two potentially uninitialized variables involving access rights. An attacker can exploit these coding errors to bypass the access control list and gain access to protected files [xorl 2009].
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
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2009].
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
Key here (explains table format and definitions)
Taxonomy | Taxonomy item | Relationship |
|---|---|---|
| CERT C Secure Coding Standard | MSC00-C. Compile cleanly at high warning levels | Prior to 2018-01-12: CERT: Unspecified Relationship |
| CERT C Secure Coding Standard | MSC01-C. Strive for logical completeness | Prior to 2018-01-12: CERT: Unspecified Relationship |
| CERT C | EXP53-CPP. Do not read uninitialized memory | Prior to 2018-01-12: CERT: Unspecified Relationship |
| ISO/IEC TR 24772:2013 | Initialization of Variables [LAV] | Prior to 2018-01-12: CERT: Unspecified Relationship |
| ISO/IEC TS 17961 | Referencing uninitialized memory [uninitref] | Prior to 2018-01-12: CERT: Unspecified Relationship |
| CWE 2.11 | CWE-456 | 2017-07-05: CERT: Exact |
| CWE 2.11 | CWE-457 | 2017-07-05: CERT: Exact |
| CWE 2.11 | CWE-758 | 2017-07-05: CERT: Rule subset of CWE |
| CWE 2.11 | CWE-908 | 2017-07-05: CERT: Rule subset of CWE |
CERT-CWE Mapping Notes
Key here for mapping notes
CWE-119 and EXP33-C
- Intersection( CWE-119, EXP33-C) = Ø
- EXP33-C is about reading uninitialized memory, but this memory is considered part of a valid buffer (on the stack, or returned by a heap function). No buffer overflow is involved.
CWE-676 and EXP33-C
- Intersection( CWE-676, EXP33-C) = Ø
- EXP33-C implies that memory allocation functions (e.g., malloc()) are dangerous because they do not initialize the memory they reserve. However, the danger is not in their invocation, but rather reading their returned memory without initializing it.
CWE-758 and EXP33-C
Independent( INT34-C, INT36-C, MSC37-C, FLP32-C, EXP33-C, EXP30-C, ERR34-C, ARR32-C)
CWE-758 = Union( EXP33-C, list) where list =
- Undefined behavior that results from anything other than reading uninitialized memory
CWE-665 and EXP33-C
Intersection( CWE-665, EXP33-C) = Ø
CWE-665 is about correctly initializing items (usually objects), not reading them later. EXP33-C is about reading memory later (that has not been initialized).
CWE-908 and EXP33-C
CWE-908 = Union( EXP33-C, list) where list =
- Use of uninitialized items besides raw memory (objects, disk space, etc)
New CWE-CERT mappings:
CWE-123 and EXP33-C
Intersection( CWE-123, EXP33-C) = Ø
EXP33-C is only about reading uninitialized memory, not writing, whereas CWE-123 is about writing.
CWE-824 and EXP33-C
EXP33-C = Union( CWE-824, list) where list =
- Read of uninitialized memory that does not represent a pointer
Bibliography
| [Flake 2006] | ||
| [ISO/IEC 9899:20112024] | Subclause 6.7.911, "Initialization" Subclause 6.2.6.1, "General" Subclause 6.3.2.1, "Lvalues, Arrays, and Function Designators" | |
| [Mercy 2006] | ||
| [VU#925211] | ||
| [Wang 2012] | "More Randomness or Less" | |
| [xorl 2009] | "CVE-2009-1888: SAMBA ACLs Uninitialized Memory Read" |
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