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fix(pdf): reject unsafe font encodings #122

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Merged
McanKul merged 1 commit into from
Oct 4, 2026
Merged

fix(pdf): reject unsafe font encodings #122

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42 changes: 42 additions & 0 deletions src-tauri/src/pdf_engine/source_content.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,8 @@ struct Flags {
no_tounicode: bool,
missing_font: bool,
ambiguous: bool,
subset_font: bool,
custom_encoding: bool,
masked: bool,
shared: bool,
geometry: bool,
Expand Down Expand Up @@ -256,6 +258,8 @@ struct TextInspect {
vertical: bool,
no_tounicode: bool,
ambiguous: bool,
subset_font: bool,
custom_encoding: bool,
width: f64,
font_id: ObjectId,
}
Expand Down Expand Up @@ -618,6 +622,8 @@ impl Walker<'_> {
no_tounicode: inspect.no_tounicode,
missing_font: inspect.missing_font,
ambiguous: inspect.ambiguous,
subset_font: inspect.subset_font,
custom_encoding: inspect.custom_encoding,
masked: gs.masked,
geometry: geom_unsafe,
..Flags::default()
Expand Down Expand Up @@ -798,6 +804,10 @@ fn pick_reason(flags: &Flags) -> (SourceCapability, Option<String>) {
Some("NO_TOUNICODE")
} else if flags.ambiguous {
Some("AMBIGUOUS_UNICODE")
} else if flags.subset_font {
Some("SUBSET_FONT")
} else if flags.custom_encoding {
Some("CUSTOM_ENCODING")
} else if flags.masked {
Some("MASKED_IMAGE")
} else if flags.shared {
Expand Down Expand Up @@ -1010,10 +1020,14 @@ fn inspect_text(
let mut vertical = false;
let mut no_tounicode = false;
let mut ambiguous = false;
let mut subset_font = false;
let mut custom_encoding = false;
let mut width_sum = 0.0;
if let Some(font) = dict {
type3 = is_type3(font);
vertical = is_vertical(doc, font);
subset_font = is_subset_font(doc, font);
custom_encoding = !is_cid_or_type0(font) && has_custom_encoding(doc, font);
if is_cid_or_type0(font) {
if tounicode_usable(doc, font) {
ambiguous = true;
Expand All @@ -1036,6 +1050,8 @@ fn inspect_text(
vertical,
no_tounicode,
ambiguous,
subset_font,
custom_encoding,
width: (width_sum + tj_adj) / 1000.0 * size,
font_id,
}
Expand All @@ -1046,6 +1062,32 @@ fn is_type3(font: &Dictionary) -> bool {
|| font.get(b"CharProcs").is_ok()
}

fn is_subset_font(doc: &Document, font: &Dictionary) -> bool {
let Ok(Object::Name(name)) = font.get_deref(b"BaseFont", doc) else {
return false;
};
name.len() > 7
&& name.get(6) == Some(&b'+')
&& name[..6].iter().all(u8::is_ascii_uppercase)
}

fn has_custom_encoding(doc: &Document, font: &Dictionary) -> bool {
if font.get(b"Encoding").is_err() {
return false;
}
let Ok(encoding) = font.get_deref(b"Encoding", doc) else {
return true;
};
!matches!(
encoding,
Object::Name(name)
if matches!(
name.as_slice(),
b"StandardEncoding" | b"WinAnsiEncoding" | b"MacRomanEncoding"
)
)
}

fn is_cid_or_type0(font: &Dictionary) -> bool {
match font.get(b"Subtype").ok().and_then(|o| o.as_name().ok()) {
Some(b"Type0") | Some(b"CIDFontType0") | Some(b"CIDFontType2") => return true,
Expand Down
92 changes: 91 additions & 1 deletion src-tauri/src/pdf_engine/source_content_integ.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,8 @@ const FILE_CAP_BYTES: u64 = 400 * 1024 * 1024;

const FROZEN_REASONS: &[&str] = &[
"MISSING_FONT",
"SUBSET_FONT",
"CUSTOM_ENCODING",
"NO_TOUNICODE",
"AMBIGUOUS_UNICODE",
"TYPE3",
Expand Down Expand Up @@ -784,6 +786,73 @@ fn classify_missing_font_is_not_supported() {
assert_eq!(reason_code(&hits[0]).as_deref(), Some("MISSING_FONT"));
}

#[test]
fn classify_subset_and_custom_encoded_fonts_are_not_supported() {
let scratch = Scratch::new("review-font-compatibility");

let mut subset = Dictionary::new();
subset.set("Type", "Font");
subset.set("Subtype", "Type1");
subset.set("BaseFont", "ABCDEF+Helvetica");
let subset_path = scratch.file("subset.pdf");
write_text_page_with_font(
&subset_path,
b"BT /F1 12 Tf 72 400 Td (Hi) Tj ET",
subset,
);
let subset_hits = classify(&subset_path, "REVIEW-SUBSET-FONT");
assert_unsupported(
first_of_kind(&subset_hits, "text", "REVIEW-SUBSET-FONT"),
"text",
"SUBSET_FONT",
"REVIEW-SUBSET-FONT",
);

let mut differences = Dictionary::new();
differences.set("Type", "Encoding");
differences.set("BaseEncoding", "WinAnsiEncoding");
differences.set(
"Differences",
vec![Object::Integer(72), Object::Name(b"customH".to_vec())],
);
let mut custom = Dictionary::new();
custom.set("Type", "Font");
custom.set("Subtype", "Type1");
custom.set("BaseFont", "Helvetica");
custom.set("Encoding", differences);
let custom_path = scratch.file("custom-encoding.pdf");
write_text_page_with_font(
&custom_path,
b"BT /F1 12 Tf 72 400 Td (Hi) Tj ET",
custom,
);
let custom_hits = classify(&custom_path, "REVIEW-CUSTOM-ENCODING");
assert_unsupported(
first_of_kind(&custom_hits, "text", "REVIEW-CUSTOM-ENCODING"),
"text",
"CUSTOM_ENCODING",
"REVIEW-CUSTOM-ENCODING",
);
}

#[test]
fn classify_named_standard_encoding_remains_supported() {
let scratch = Scratch::new("review-standard-encoding");
let path = scratch.file("win-ansi.pdf");
let mut font = Dictionary::new();
font.set("Type", "Font");
font.set("Subtype", "Type1");
font.set("BaseFont", "Helvetica");
font.set("Encoding", "WinAnsiEncoding");
write_text_page_with_font(&path, b"BT /F1 12 Tf 72 400 Td (Hi) Tj ET", font);
let hits = classify(&path, "REVIEW-STANDARD-ENCODING");
assert_supported_text_or_image(
first_of_kind(&hits, "text", "REVIEW-STANDARD-ENCODING"),
"text",
"REVIEW-STANDARD-ENCODING",
);
}

#[test]
fn classify_repeated_form_occurrences_have_unique_locators() {
let scratch = Scratch::new("review-repeated-form");
Expand Down Expand Up @@ -823,15 +892,36 @@ fn write_helvetica_page(path: &Path, content: &[u8]) {
}

fn write_helvetica_page_with_stream_dict(path: &Path, content: &[u8], stream_dict: Dictionary) {
let mut font = Dictionary::new();
font.set("Type", "Font");
font.set("Subtype", "Type1");
font.set("BaseFont", "Helvetica");
write_text_page_with_font_and_stream_dict(path, content, font, stream_dict);
}

fn write_text_page_with_font(path: &Path, content: &[u8], font: Dictionary) {
write_text_page_with_font_and_stream_dict(path, content, font, Dictionary::new());
}

fn write_text_page_with_font_and_stream_dict(
path: &Path,
content: &[u8],
font: Dictionary,
stream_dict: Dictionary,
) {
let mut doc = Document::with_version("1.7");
let pages_id = doc.new_object_id();
let content_id = doc.add_object(Object::Stream(Stream::new(stream_dict, content.to_vec())));
let mut fonts = Dictionary::new();
fonts.set("F1", Object::Dictionary(font));
let mut resources = Dictionary::new();
resources.set("Font", Object::Dictionary(fonts));
let mut page = Dictionary::new();
page.set("Type", "Page");
page.set("Parent", pages_id);
page.set("MediaBox", box_obj([0, 0, 612, 792]));
page.set("Contents", content_id);
page.set("Resources", Object::Dictionary(helvetica_resources()));
page.set("Resources", Object::Dictionary(resources));
let page_id = doc.add_object(Object::Dictionary(page));

let mut pages = Dictionary::new();
Expand Down
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