Out-of-Bounds Read in FlatCC Schema Lexer

Executive Summary

This is an out-of-bounds read vulnerability in the flatcc library's schema lexer. When a FlatBuffers schema buffer ends with a digit, the lexer's integer digit-scan loop reads one byte past the buffer's end, causing a heap buffer over-read. This leads to application crashes, denial of service, or potential heap leaks.

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Detection Guidance

To detect this vulnerability, monitor applications using flatcc for crashes or memory errors when processing FlatBuffers schemas with trailing digits. Use tools like AddressSanitizer or Valgrind to detect heap buffer over-reads. Example commands: 1) Compile flatcc with AddressSanitizer: CC="clang -fsanitize=address" ./configure && make. 2) Run flatcc on a test schema with a trailing digit to trigger the issue. 3) Use Valgrind: valgrind --tool=memcheck flatcc test_schema.fbs.

Check for crashes in applications linked against flatcc when parsing schemas ending with numbers. Review logs for segmentation faults or memory access violations.

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Impact Analysis

This vulnerability can cause applications using flatcc to crash or become unresponsive, leading to denial of service. It may also expose sensitive memory contents or enable further exploitation through heap manipulation.

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Compliance Impact

This vulnerability could indirectly impact compliance with standards like GDPR or HIPAA by enabling denial-of-service attacks through application crashes. Such attacks may disrupt services handling sensitive data, potentially violating availability requirements in these regulations.

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Mitigation Strategies

Immediately update flatcc to the patched version that includes the fix for the lexer buffer boundary check. If updating is not possible, apply the patch manually from the upstream commit c1dcc8e. Temporarily avoid processing FlatBuffers schemas with trailing digits until patched.

Monitor applications using flatcc for crashes or memory errors. Consider disabling or isolating services using flatcc if the vulnerability is actively exploited.

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