The C standard identifies specific strings to use for the mode on calls to fopen() [[ISO/IEC 9899-1999]] . To be strictly conforming and portable, one of the strings from the following table (adapted from the C standard) must be used:
|
Result |
|---|---|
r |
open text file for reading |
w |
truncate to zero length or create text file for writing |
a |
append; open or create text file for writing at end-of-file |
rb |
open binary file for reading |
wb |
truncate to zero length or create binary file for writing |
ab |
append; open or create binary file for writing at end-of-file |
r+ |
open text file for update (reading and writing) |
w+ |
truncate to zero length or create text file for update |
a+ |
append; open or create text file for update, writing at end-of-file |
r+b or rb+ |
open binary file for update (reading and writing) |
w+b or wb+ |
truncate to zero length or create binary file for update |
a+b or ab+ |
append; open or create binary file for update, writing at end-of-file |
If the mode string begins with one of the above sequences, the implementation might choose to ignore the
remaining characters, or it might use them to select different kinds of a file.
An implementation may define additional mode strings, but only the modes in the above table are fully portable and C99 compliant.
Risk Assessment
Using a mode string that is not recognized by an implementation may cause the call to fopen() to fail.
Recommendation |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
FIO11-A |
1 (low) |
2 (probable) |
3 (low) |
P6 |
L2 |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
[[ISO/IEC 9899-1999]] Section 7.9.15.3, "The fopen function"
FIO10-A. Take care when using the rename() function 09. Input Output (FIO) FIO12-A. Prefer setvbuf() to setbuf()