UPSTREAM PR #26908: java: limit numeric string length before BigDecimal parsing#141
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UPSTREAM PR #26908: java: limit numeric string length before BigDecimal parsing#141loci-dev 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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No meaningful performance changes were detected across 10167 analyzed functions in the following binaries: build.protoc-stable. 💬 Questions? Tag @loci-dev |
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String.repeat() was added in Java 11. Use a StringBuilder loop instead to maintain Java 8 compatibility per project requirements.
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Source pull request: protocolbuffers/protobuf#26908
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.