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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The realloc() function changes the size of a dynamically allocated memory object. The initial size bytes of the returned memory object are unchanged, but any newly added space is uninitialized, and its value is indeterminate. As in the case of malloc(), accessing memory beyond the size of the original object is undefined behavior 181186.
It is the programmer's responsibility to ensure that any memory allocated with malloc() and realloc() is properly initialized before it is used.
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| Tool | Version | Checker | Description | |||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Astrée |
| uninitialized-local-read uninitialized-variable-use | Fully checked | |||||||||||||||||||||||||||||||||||||||||||||
| Axivion Bauhaus Suite |
| CertC-EXP33 | ||||||||||||||||||||||||||||||||||||||||||||||
| CodeSonar |
| LANG.MEM.UVAR | Uninitialized variable | |||||||||||||||||||||||||||||||||||||||||||||
| Compass/ROSE | 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 |
| Helix QAC
| Helix QAC
| C2726, C2727, C2728, C2961, C2962, C2963, C2966, C2967, C2968, C2971, C2972, C2973, C2976, C2977, C2978 | Klocwork | |||||||||||||||||||||||||||||||||||||||||||
| Include Page | Klocwork_V | Klocwork_V | UNINIT.HEAP.MIGHT | 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 | LDRA tool suite | |||||||||||||||||||||||||||||||||||||||||||||
| Include Page | LDRA_V | LDRA_V | 53 D, 69 D, 631 S, 652 S | Fully implemented | Parasoft C/C++test | |||||||||||||||||||||||||||||||||||||||||||
| Include Page | Parasoft_V | Parasoft_V | CERT_C-EXP33-a | Avoid use before initialization | Parasoft Insure++ | |||||||||||||||||||||||||||||||||||||||||||
| Include Page | Parasoft_V | Parasoft_V | Runtime analysis | PC-lint Plus | ||||||||||||||||||||||||||||||||||||||||||||
| Include Page | PC-lint Plus_V | PC-lint Plus_V | 530, 603, 644, 901 | Fully supported | Polyspace Bug Finder | |||||||||||||||||||||||||||||||||||||||||||
| Include Page | Polyspace Bug Finder_V | Polyspace Bug Finder_V | Checks for:
Rule partially covered | PRQA QA-C | ||||||||||||||||||||||||||||||||||||||||||||
| Include Page | PRQA QA-C_v | PRQA QA-C_v | 2726, 2727, 2728, 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 | |||||||||||||||||||||||||||||||||||||||
| 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 attacker can exploit these coding errors to bypass the access control list and gain access to protected files [xorl 2009].
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| [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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