fix(gif): reject a short graphics-control extension block - #5366
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read_gif_extension() read ext[1..4] from the graphics-control block without checking ext[0], the sub-block byte count. A corrupt file can declare fewer than the 4 bytes a well-formed block carries, so bail before reading past the giflib-provided buffer. Assisted-by: GitHub Copilot / Claude Opus 4.8 Signed-off-by: Larry Gritz <lg@larrygritz.com>
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read_gif_extension() read ext[1..4] from the graphics-control block without checking ext[0], the sub-block byte count. A corrupt file can declare fewer than the 4 bytes a well-formed block carries, so bail before reading past the giflib-provided buffer.
Assisted-by: GitHub Copilot / Claude Opus 4.8