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Review fix-up: only CFB files with an EncryptedPackage are encrypted

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Every legacy .xls/.doc is a CFB/OLE2 file, so the signature alone isn't encryption. Walk the
compound file's directory (bounds-checked, bounded loops; raw UTF-16 scan when the structure
is unreadable) and report Encrypted only for an EncryptedPackage/EncryptionInfo stream;
other compound files are LegacyBinary with a "save as .xlsx" message. Tests build CFB bytes
in code.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Brandon Thomas
2026-10-10 12:35:36 -04:00
co-authored by Claude Opus 5.5
parent 9365c5a9c6
commit f041904bf8
4 changed files with 216 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/engine/src/io.rs
+37 -3
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@@ -41,6 +41,11 @@ pub fn open_bytes(name: &str, bytes: &[u8]) -> Result<(Workbook, Vec<String>)> {
"'{name}' is password-protected. GridCraft can't open encrypted workbooks yet; remove the password in Excel and try again."
)));
}
if sniffed == gridcraft_xlsx::Format::LegacyBinary {
return Err(EngineError::Other(format!(
"'{name}' is an Excel 97-2003 (.xls) workbook or another legacy binary file. GridCraft doesn't open these yet; save it as .xlsx in Excel and try again."
)));
}
if sniffed == gridcraft_xlsx::Format::Xlsx || kind == Some(FileKind::Xlsx) {
let (wb, report) = gridcraft_xlsx::read_xlsx(bytes).map_err(|e| EngineError::Other(format!("We can't open '{name}': {e}")))?;
return Ok((wb, report.warnings));
@@ -254,13 +259,42 @@ pub fn image_size(data: &[u8]) -> Option<(u32, u32)> {
mod tests {
use super::*;
/// A minimal compound (CFB/OLE2) file — FAT in sector 0, directory in sector 1 — holding a
/// root entry and the given stream names.
fn cfb(streams: &[&str]) -> Vec<u8> {
let mut b = vec![0u8; 512 * 3];
let mut put = |at: usize, v: &[u8]| b[at..at + v.len()].copy_from_slice(v);
put(0, &[0xD0, 0xCF, 0x11, 0xE0, 0xA1, 0xB1, 0x1A, 0xE1]);
put(30, &9u16.to_le_bytes());
put(44, &1u32.to_le_bytes());
put(48, &1u32.to_le_bytes());
put(68, &0xFFFF_FFFEu32.to_le_bytes());
for i in 1..109 {
put(76 + i * 4, &0xFFFF_FFFFu32.to_le_bytes());
}
put(512, &0xFFFF_FFFDu32.to_le_bytes());
put(516, &0xFFFF_FFFEu32.to_le_bytes());
for (k, name) in std::iter::once("Root Entry").chain(streams.iter().copied()).enumerate() {
let units: Vec<u8> = name.encode_utf16().flat_map(u16::to_le_bytes).collect();
put(1024 + k * 128, &units);
put(1024 + k * 128 + 64, &(units.len() as u16 + 2).to_le_bytes());
}
b
}
#[test]
fn encrypted_workbook_is_reported_not_misread() {
// A CFB/OLE2 header: Excel's password-protected container.
let cfb = [0xD0, 0xCF, 0x11, 0xE0, 0xA1, 0xB1, 0x1A, 0xE1, 0, 0, 0, 0];
let err = open_bytes("secret.xlsx", &cfb).unwrap_err();
let err = open_bytes("secret.xlsx", &cfb(&["EncryptionInfo", "EncryptedPackage"])).unwrap_err();
let msg = err.to_string();
assert!(msg.contains("password-protected"), "got: {msg}");
assert!(!msg.contains("zip"), "must not surface the zip error: {msg}");
}
#[test]
fn legacy_xls_is_not_called_encrypted() {
let err = open_bytes("old.xls", &cfb(&["Workbook", "\u{5}SummaryInformation"])).unwrap_err();
let msg = err.to_string();
assert!(msg.contains("97-2003") && msg.contains(".xlsx"), "got: {msg}");
assert!(!msg.contains("password"), "got: {msg}");
}
}