[LANG-1286] RandomStringUtils random method can overflow and return characters outside of specified range

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.5
• Fix Version/s: 3.6
• Component/s: lang.*
• Assignee: Duncan Jones
• Reporter: Duncan Jones
• Created: 17/Nov/16 21:00
• Updated: 14/Dec/16 06:34
• Resolved: 14/Dec/16 06:34

Description

RandomStringUtils.random() can overflow and return characters that are outside the range specified by the start and end parameters. This is because it casts a random integer in the range [start,end) to a character, without checking if this will overflow.

Example failing test case:

@Test
public void testCharOverflow() throws Exception {
    int start = 65535;
    int end = Integer.MAX_VALUE;
    
    @SuppressWarnings("serial")
    Random fixedRandom = new Random() {
        @Override
        public int nextInt(int n) {
            // Prevents selection of 'start' as the character
            return 1;
        }
    };
    
    String result = RandomStringUtils.random(1, start, end, false, false, null, fixedRandom);
    char c = result.charAt(0);
    assertTrue(c >= start && c < end);
}