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Java does not support the use of unsigned types, except for the 16 bit char datatype. Sometimes, it is necessary to The only unsigned primitive integer type in Java is the 16-bit char data type; all of the other primitive integer types are signed. To interoperate with native languages, such as C or C++, that use unsigned types extensively. The standard practice to deal with unsigned input is to read values into Java's larger signed primitives, any unsigned values must be read and stored into a Java integer type that can fully represent the possible range of the unsigned data. For example, a signed the Java long type can be used to hold an unsigned integer represent all possible unsigned 32-bit integer values obtained from native code.

Noncompliant Code Example

This noncompliant code example incorrectly uses a generic method for reading in integer data irrespective without considering the signedness of the signednesssource. It assumes that the value data read is always signed and treats the most significant bit (MSB) as the sign bit causing misinterpretations about . When the data read is unsigned, the actual sign and magnitude of the integervalues may be misinterpreted.

public static int getInteger(DataInputStream is) throws IOException {
  return is.readInt();	
}

Compliant Solution

This compliant solution assumes requires that the unsigned integer has 32 bitsvalues read are 32-bit unsigned integers. It reads in an unsigned integer value into a long variable using the readInt() method. If the read integer is unsigned, the most significant bit may be turned on. Consequently, all the higher order bits of the resulting long are set because of sign extension, and these must be masked off as demonstrated. For other integer sizes, the mask size should vary depending on The readInt() method assumes signed values and returns a signed int; the return value is converted to a long with sign extension. The code uses an & operation to mask off the upper 32 bits of the long, producing a value in the range of a 32-bit unsigned integer, as intended. The mask size should be chosen to match the size of the unsigned integer values being read.

public static long getInteger(DataInputStream is) throws IOException {
  return is.readInt() & 0xFFFFFFFFL;	 // Mask with 32 one-bits
}

As a general principle, you should always be aware of the signedness of the data you are reading.

Risk Assessment

Treating an unsigned type data as signed can result in misinterpretations though it were signed produces incorrect values and can lead to lost or misinterpreted data.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this guideline on the CERT websiteAutomated detection is infeasible in the general case.

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[Seacord 2015]	Image Added NUM03-J. Use integer types that can fully represent the possible range of unsigned data LiveLesson

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Image Added Image Added Image AddedINT07-J. Provide methods to read and write little-endian data      06. Integers (INT)      INT09-J. Do not rely on the write() method to output integers outside the range 0 to 255