FIO03-J. Specify the character encoding while performing file or network IO

Every Java platform has a default character encoding. The codings available are listed in [[Encodings 06]]. The default encoding is used when a character is converted to a sequence of bytes and vice versa. If characters are being converted into an array of bytes, output, transmitted across some medium, input, and converted back into characters then it is clearly important that the same encoding is used on both side of the conversion.

Also, see FIO02-J. Keep track of bytes read and account for character encoding while reading data.

Noncompliant Code Example

In this noncompliant code example, a byte array is read and converted into a string using the default character encoding for the platform. If this is not the same encoding as was used to produce the byte array then the resulting string will be garbage because the some of the bytes may not have valid character representations in the default encoding.

FileInputStream fis = new FileInputStream("SomeFile");
DataInputStream dis = new DataInputStream(fis);
int bytesRead = 0;
byte[] data = new byte[1024];

bytesRead = dis.readFully(data);

if (bytesRead > 0) {
   String result = new String(data);
}

Compliant Solution

In this compliant solution, the encoding is explicitly specified by using the string encoding as the second parameter of the String constructor.

String encoding = "SomeEncoding" // for example, "UTF-16LE"

FileInputStream fis = new FileInputStream("SomeFile");
DataInputStream dis = new DataInputStream(fis);
int bytesRead = 0;
byte[] data = new byte[1024];

bytesRead = dis.readFully(data);

if (bytesRead > 0) {
   String result = new String(data, encoding);
}

Exceptions

*EX1:* If the data is coming from another Java application on the same platform and it is known that that application is using the default character encoding, then an explicit character encoding does not need to be specified on the receiving side.

Risk Assessment

Automated Detection

TODO

Related Vulnerabilities

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

References

[[Encodings 06]]

FIO02-J. Keep track of bytes read and account for character encoding while reading data      08. Input Output (FIO)      FIO30-J. Do not log sensitive information