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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.

See undefined behavior 11.

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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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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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Key here (explains table format and definitions)

CERT-CWE Mapping Notes

Key here for mapping notes

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• Read of uninitialized memory that does not represent a pointer

Bibliography

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