java: limit numeric string length before BigDecimal parsing#26908
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java: limit numeric string length before BigDecimal parsing#26908MindflareX wants to merge 2 commits into
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BigDecimal(String) has O(N^2) time complexity for N-digit strings on JDK versions before 18 (JDK-8291514). The JSON parser passes user-controlled strings directly to BigDecimal in parseInt32, parseInt64, parseUint32, parseUint64, and parseDouble, allowing a single long numeric value to consume seconds of CPU. Add a parseBigDecimal helper that rejects strings longer than 1000 characters before constructing BigDecimal. This is generous — valid protobuf numeric values never exceed ~350 characters.
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| public void testParserRejectOverlyLongNumericStrings() throws Exception { | ||
| // A numeric string with 10,000 digits should be rejected quickly to prevent | ||
| // O(N^2) BigDecimal parsing DoS. | ||
| String longNumber = "1" + "0".repeat(10000); |
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Unfortunately you need to avoid using .repeat() here since our min support is java8 and .repeat() was only added after
Thanks!
String.repeat() was added in Java 11. Use a StringBuilder loop instead to maintain Java 8 compatibility per project requirements.
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Summary
BigDecimal(String)has O(N²) time complexity for N-digit strings on JDK versions before 18 (JDK-8291514). Five JSON parser methods —parseInt32,parseInt64,parseUint32,parseUint64, andparseDouble— pass user-controlled strings directly tonew BigDecimal()without length validation.A single JSON numeric value with 1,000,000 digits takes ~13 seconds to parse on JDK 17. This can be used to DoS any service that parses protobuf JSON messages with numeric fields from untrusted input.
Benchmark (JDK 17, x86-64 Linux)
Fix
Added a
parseBigDecimal()helper that rejects strings longer than 1000 characters before constructingBigDecimal. This is generous — valid protobuf numeric values never exceed ~350 characters (Double.MAX_VALUE in non-scientific notation is ~309 digits).Affected JDK versions
Test
Added
testParserRejectOverlyLongNumericStringscovering all 5 affected field types.