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‎cpp/ql/src/experimental/Security/CWE/CWE-200/ExposureSensitiveInformationUnauthorizedActor.cpp‎

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...
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FILE *fp = fopen(filename,"w"); // BAD
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...
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umask(S_IXUSR|S_IRWXG|S_IRWXO);
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FILE *fp;
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fp = fopen(filename,"w"); // GOOD
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chmod(filename,S_IRUSR|S_IWUSR);
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fprintf(fp,"%s\n","data to file");
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fclose(fp);
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...

‎cpp/ql/src/experimental/Security/CWE/CWE-200/ExposureSensitiveInformationUnauthorizedActor.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>Finding for places to work with files without restrictions on access rights.</p>
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</overview>
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<example>
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<p>The following example demonstrates erroneous and fixed methods for working with files.</p>
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<sample src="ExposureSensitiveInformationUnauthorizedActor.cpp" />
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</example>
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<references>
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<li>
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CERT C Coding Standard:
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<a href="https://wiki.sei.cmu.edu/confluence/display/c/FIO06-C.+Create+files+with+appropriate+access+permissions">FIO06-C. Create files with appropriate access permissions</a>.
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</li>
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</references>
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</qhelp>

‎cpp/ql/src/experimental/Security/CWE/CWE-200/ExposureSensitiveInformationUnauthorizedActor.ql‎

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/**
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* @name Find work with the file without setting permissions.
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* @description Lack of restriction on file access rights can be unsafe.
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* @kind problem
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* @id cpp/work-with-file-without-permissions-rights
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* @problem.severity warning
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* @precision medium
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* @tags correctness
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* maintainability
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* security
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* external/cwe/cwe-200
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* external/cwe/cwe-264
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*/
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import cpp
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import semmle.code.cpp.valuenumbering.GlobalValueNumbering
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/** Holds for a function `f` that has an argument at index `apos` used to read the file. */
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predicate numberArgumentRead(Function f, int apos) {
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f.hasGlobalOrStdName("fgets") and apos = 2
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or
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f.hasGlobalOrStdName("fread") and apos = 3
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or
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f.hasGlobalOrStdName("read") and apos = 0
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or
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f.hasGlobalOrStdName("fscanf") and apos = 0
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}
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/** Holds for a function `f` that has an argument at index `apos` used to write to file */
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predicate numberArgumentWrite(Function f, int apos) {
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f.hasGlobalOrStdName("fprintf") and apos = 0
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or
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f.hasGlobalOrStdName("fputs") and apos = 1
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or
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f.hasGlobalOrStdName("write") and apos = 0
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or
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f.hasGlobalOrStdName("fwrite") and apos = 3
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or
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f.hasGlobalOrStdName("fflush") and apos = 0
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}
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from FunctionCall fc
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where
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(
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fc.getTarget().hasGlobalOrStdName("fopen") or
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fc.getTarget().hasGlobalOrStdName("open")
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) and
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fc.getNumberOfArguments() = 2 and
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exists(FunctionCall fctmp, int i |
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numberArgumentWrite(fctmp.getTarget(), i) and
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globalValueNumber(fc) = globalValueNumber(fctmp.getArgument(i))
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) and
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not exists(FunctionCall fctmp, int i |
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numberArgumentRead(fctmp.getTarget(), i) and
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globalValueNumber(fc) = globalValueNumber(fctmp.getArgument(i))
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) and
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not exists(FunctionCall fctmp |
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fctmp.getTarget().hasGlobalOrStdName("umask") or
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fctmp.getTarget().hasGlobalOrStdName("fchmod") or
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fctmp.getTarget().hasGlobalOrStdName("chmod")
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) and
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not exists(FunctionCall fctmp |
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fctmp.getTarget().hasGlobalOrStdName("fdopen") and
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fctmp.getNumberOfArguments() = 3 and
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globalValueNumber(fctmp) = globalValueNumber(fc.getArgument(0))
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)
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select fc, "You may have forgotten to restrict access rights when working with a file."

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