Skip to content

Fix GIF background color index bounds #570

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
treeform merged 1 commit into from
Apr 30, 2026
Merged

Fix GIF background color index bounds #570

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion src/pixie/fileformats/gif.nim
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
bgColorIndex = data.readUint8(11).int
pixelAspectRatio = data.readUint8(12)

if bgColorIndex > globalColorTableSize:
if bgColorIndex >= globalColorTableSize:
failInvalid()

if pixelAspectRatio != 0:
Expand Down
17 changes: 17 additions & 0 deletions tests/test_gif.nim
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -35,3 +35,20 @@ block:
decodeGif(readFile("tests/fileformats/gif/newtons_cradle.gif"))
doAssert animatedGif.frames.len == 36
doAssert animatedGif.intervals.len == animatedGif.frames.len

block:
proc addLe16(data: var string, value: int) =
data.add(char(value and 0xff))
data.add(char((value shr 8) and 0xff))

var payload = "GIF89a"
payload.addLe16(1)
payload.addLe16(1)
payload.add(char(0x80)) # Global color table present, size = 2 entries.
payload.add(char(0x02)) # One past the last valid color table index.
payload.add(char(0x00))
payload.add("\x00\x00\x00\xff\xff\xff")
payload.add(char(0x3b))

doAssertRaises PixieError:
discard decodeGif(payload)