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harden VBA dir-stream parsing + bound decompression; pre-size ReadChain #12

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harden VBA dir-stream parsing + bound decompression; pre-size ReadChain #12

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17 changes: 15 additions & 2 deletions limits.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,19 @@ const (
// Limit the size of the document
MAX_SECTORS = 1024 * 1024

sectorShiftV3 = 0x9
sectorShiftV4 = 0xC
sectorShiftV3 = 0x9
sectorShiftV4 = 0xC
miniSectorShift = 0x6

// MAX_DECOMPRESSED bounds DecompressStream output. MS-OVBA copy tokens can
// expand a 4096-byte chunk window repeatedly; a crafted input could
// otherwise amplify to tens of GiB and OOM the process. Legit VBA dir/source
// streams are well under this.
MAX_DECOMPRESSED = 32 * 1024 * 1024 // 32 MiB

// MAX_MODULES caps the VBA project module count. The uint16 field is already
// dir_stream-bounded, but a generous explicit cap stops a degenerate
// high-count header from driving a long parse loop (kept generous; real
// projects are <<4096 modules).
MAX_MODULES = 4096
)
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