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[LANG-1801] Fix RandomStringUtils.random() does not strictly validate start/end when chars != null, causing potential IndexOutOfBoundsException #1521

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[LANG-1801] Fix RandomStringUtils.random() does not strictly validate start/end when chars != null, causing potential IndexOutOfBoundsException #1521

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105f2b5
RandomStringUtils.random() does not strictly validate start/end when …
IcoreE Dec 9, 2025
4413cb5
Merge branch 'apache:master' into fix_RandomStringUtils#random_IndexO…
IcoreE Dec 13, 2025
ca327ab
Run mvn and adjust the code style
IcoreE Dec 21, 2025
9168446
Merge branch 'master' into fix_RandomStringUtils#random_IndexOutOfBou…
IcoreE Dec 21, 2025
4b55a30
[LANG-1801] Add additional unit test
IcoreE Dec 22, 2025
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13 changes: 13 additions & 0 deletions src/main/java/org/apache/commons/lang3/RandomStringUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -278,6 +278,19 @@ public static String random(int count, int start, int end, final boolean letters
"Parameter end (" + end + ") must be greater than start (" + start + ")");
} else if (start < 0 || end < 0) {
throw new IllegalArgumentException("Character positions MUST be >= 0");
} else if (chars != null && (start >= chars.length || end > chars.length)) {
final StringBuilder errorMsg = new StringBuilder();
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@garydgregory garydgregory Mar 17, 2026

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This is all too complicated IMO, we don't gather all possible invalid inputs elsewhere in the method. Please rebase on git master, fail-fast and use String.format(), so that would end up being 2 throws.

final int charsLength = chars.length;
if (start >= charsLength) {
errorMsg.append("Parameter start (").append(start).append(") must be less than chars array length ").append(charsLength);
}
if (end > charsLength) {
if (errorMsg.length() > 0) {
errorMsg.append("; ");
}
errorMsg.append("Parameter end (").append(end).append(") must be less than or equal to chars array length ").append(charsLength);
}
throw new IllegalArgumentException(errorMsg.toString());
}

if (end > Character.MAX_CODE_POINT) {
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2 changes: 2 additions & 0 deletions src/test/java/org/apache/commons/lang3/RandomStringUtilsTest.java
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Expand Up @@ -104,6 +104,8 @@ void testExceptionsRandom() {
assertIllegalArgumentException(() -> RandomStringUtils.random(8, 32, 48, false, true));
assertIllegalArgumentException(() -> RandomStringUtils.random(8, 32, 65, true, false));
assertIllegalArgumentException(() -> RandomStringUtils.random(1, Integer.MIN_VALUE, -10, false, false, null));
assertIllegalArgumentException(() -> RandomStringUtils.random(2, 4, 5, false, false, new char[] { 'a', 'b', 'c', 'd' }, new Random()));
assertIllegalArgumentException(() -> RandomStringUtils.random(2, 1, 5, false, false, new char[] { 'a', 'b', 'c', 'd' }, new Random()));
}

@ParameterizedTest
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