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These functions truncate strings that exceed the specified limits. Additionally, some functions such as strncpy() do not guarantee that the resulting string is null-terminated. (see See guideline STR32-C. Null-terminate byte strings as required.).

Unintentional truncation results in a loss of data and, in some cases, leads to software vulnerabilities.

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Either the strcpy() or strncpy() function can be used to copy a string and a null character to a destination buffer, provided there is enough space. Care must be taken to ensure that the destination buffer is large enough to hold the string to be copied and the null byte to prevent errors, such as data truncation and buffer overflow.

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This solution requires that string_data is null-terminated, ; that is, a null byte can be found within the bounds of the referenced character array. Otherwise, strlen() will stray into other objects before finding a null byte.

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The {{strcpy_s()}} function defined in \[[ISO/IEC TR 24731-1:2007|AA. Bibliography#ISO/IEC TR 24731-1-2007]\] provides additional safeguards, including accepting the size of the destination buffer as an additional argument. (seeSee guideline [STR07-C. Use TR 24731 for remediation of existing string manipulation code|STR07-C. Use TR 24731 for remediation of existing string manipulation code]). Also,].) Also {{strnlen_s()}} accepts a maximum-length argument for strings that may not be null-terminated.

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If a runtime constraint error is detected by either the call to strnlen_s() or strcpy_s(), the currently registered runtime-constraint handler is invoked. See guideline ERR03-C. Use runtime-constraint handlers when calling functions defined by TR24731-1 for more information on using runtime-constraint handlers with TR 24731-1 functions.

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Automated Detection

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Tool	Version	Checker	Description
Section LDRA tool suite	Include Page c:LDRA_V c:LDRA_V
Section Fortify SCA	Section V. 5.0		Section can detect violations of this

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rule with CERT C Rule Pack

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Section Compass/ROSE			Section could detect violations in the following manner: All calls to strncpy() and the other functions should be follwed by an assignment of a terminating character to null-terminate the string

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Section Klocwork	Include Page c:Klocwork_V c:Klocwork_V	Section NNTS

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Other Languages

Related Guidelines

This rule appears in the C++ Secure Coding Standard as : STR03-CPP. Do not inadvertently truncate a null-terminated character array.

Bibliography

\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 7.21, "String handling <string.h>"
\[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "CJM String Termination"
\[[ISO/IEC TR 24731-1:2007|AA. Bibliography#ISO/IEC TR 24731-1-2007]\]
\[[MITRE 072007|AA. Bibliography#MITRE 07]\] [CWE ID 170|http://cwe.mitre.org/data/definitions/170.html], "Improper Null Termination," [CWE ID 464|http://cwe.mitre.org/data/definitions/464.html], "Addition of Data Structure Sentinel"
\[[Seacord 05a2005a|AA. Bibliography#Seacord 05a]\] Chapter 2, "Strings"

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