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Author	SHA1	Message	Date
Christoph Wille	c685d5305b	Bound XamarinCompressedFileLoader against crafted XALZ headers The Xamarin XALZ loader sized its buffer allocations from an attacker-controlled header field and ignored the partial-read length, so merely opening a crafted file (the loader is registered first and runs on any XALZ-magic input) could crash or over-allocate. The declared uncompressed length, a raw header uint cast to int, had no sanity bound: a tiny file claiming ~2 GB forced a giant ArrayPool.Rent (decompression-bomb amplification), and a high-bit value became negative and made Rent throw ArgumentOutOfRangeException. The compressed length was taken as the whole file (header included) and ReadAsync's return value was discarded, leaving stale pooled bytes in the tail fed to the decoder; the output MemoryStream then exposed the entire rented buffer, so PEFile parsed past the real decompressed data into leftover pool contents. Bound the declared length before renting (reject zero, > int.MaxValue, or more than an LZ4 block could expand from this payload at its 255x maximum ratio), read the payload that actually follows the header with ReadExactlyAsync, and slice the output to the length LZ4Codec.Decode reports. Malformed input now fails as a catchable InvalidDataException, consistent with the bundle and .rsrc hardening; well-formed Xamarin modules load exactly as before. Assisted-by: Claude:claude-opus-4-8:Claude Code	2 months ago

Author

SHA1

Message

Date

Christoph Wille

c685d5305b

Bound XamarinCompressedFileLoader against crafted XALZ headers

The Xamarin XALZ loader sized its buffer allocations from an attacker-controlled
header field and ignored the partial-read length, so merely opening a crafted
file (the loader is registered first and runs on any XALZ-magic input) could
crash or over-allocate. The declared uncompressed length, a raw header uint cast
to int, had no sanity bound: a tiny file claiming ~2 GB forced a giant
ArrayPool.Rent (decompression-bomb amplification), and a high-bit value became
negative and made Rent throw ArgumentOutOfRangeException. The compressed length
was taken as the whole file (header included) and ReadAsync's return value was
discarded, leaving stale pooled bytes in the tail fed to the decoder; the
output MemoryStream then exposed the entire rented buffer, so PEFile parsed past
the real decompressed data into leftover pool contents.

Bound the declared length before renting (reject zero, > int.MaxValue, or more
than an LZ4 block could expand from this payload at its 255x maximum ratio),
read the payload that actually follows the header with ReadExactlyAsync, and
slice the output to the length LZ4Codec.Decode reports. Malformed input now
fails as a catchable InvalidDataException, consistent with the bundle and .rsrc
hardening; well-formed Xamarin modules load exactly as before.

Assisted-by: Claude:claude-opus-4-8:Claude Code

2 months ago

1 Commits (bfa3f1898048e7ad14f71a741f07afcf3ec2127f)