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char myFilenamemyFile name[1000]; char const elimNewLn[] = "\n"; fgets(myFilenamemyFile name, sizeof(myFilenamemyFile name)-1, stdin); myFilenamemyFile name[sizeof(myFilenamemyFile name)-1] = '\0'; myFilenamemyFile name[strcspn(myFilenamemyFile name, elimNewLn)] = '\0'; |
No checks are performed on the file name to prevent troublesome characters. If an attacker knew this code was in a program used to create or rename files that would later be used in a script or automated process of some sort, they could choose particular characters in the output file name to confuse the later process for malicious purposes.
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char myFile myFilenamename[1000]; char const elimNewln[] = "\n"; char const badChars[] = "-\n\r ,;'\\<\""; do { fgets(myFilenamemyFile name, sizeof(myFilenamemyFile name)-1, stdin); myFile myFilenamename[sizeof(myFilenamemyFile name)-1] ='\0'; myFile myFilenamename[strcspn(myFilenamemyFile name, elimNewln)]='\0'; } while ( (strcspn(myFilenamemyFile name, badChars)) < (strlen(myFilenamemyFile name))); |
Similarly, you must provide validate all file names originating from untrusted sources to ensure they contain only safe characters.
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\[[Kuhn 06|AA. C References#Kuhn 06]\] UTF-8 and Unicode FAQ for UnixUNIX/Linux \[[ISO/IEC 646-1991|AA. C References#ISO/IEC 646-1991]\] ISO 7-bit coded character set for information interchange \[[ISO/IEC 9899-:1999|AA. C References#ISO/IEC 9899-1999]\] Section 5.2.1, "Character sets" \[[MISRA 04|AA. C References#MISRA 04]\] Rule 3.2, "The character set and the corresponding encoding shall be documented," and Rule 4.1, "Only those escape sequences that are defined in the ISO C standard shall be used" \[[Wheeler 03|AA. C References#Wheeler03]\] 5.4 File Names \[[VU#881872|AA. C References#VU881872]\] |
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