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 checked | 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.) | |||||||||||||||||||||||||||
| Cppcheck Premium |
| 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. | 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 |
| BDCERT_C- | BPEXP33- | NOTINITFully implementeda | Avoid use before initialization | |||||||||||||||||||||||||
| Parasoft Insure++ |
| Runtime analysis | ||||||||||||||||||||||||||||
| Polyspace Bug Finder | R2016a | Pointer not initialized before dereference Variable not initialized before use | ||||||||||||||||||||||||||||
| PC-lint Plus |
| 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 | 530, 603, 644, 901 | Fully supported | ||||||||||||||||||||||||||
| Polyspace Bug Finder |
| Checks for:
Rule partially covered | ||||||||||||||||||||||||||||
| PVS-Studio |
| 2961, 2962, 2963, 2966, 2967, 2968, 2971, 2972, 2973, 2976, 2977, 2978 | PVS-Studio | 6.22 | V573, V614, V670, V679, V1050 | |||||||||||||||||||||||||
| RuleChecker |
| uninitialized-local-readuninitialized-variable-use | 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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