vulnerability / NVI-00010636 / Revision 1
Pillow: Invalid free in FreeType glyph rendering when a stroker is active
GitHub lists this reviewed advisory for pillow. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
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02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
pillow
source listed>= 10.0.0, < 13.0.0
### Summary When text is drawn with a non-zero stroke width, Pillow creates a FreeType stroker and then loads each glyph. If `FT_Load_Glyph` fails for a glyph, the cleanup path calls `FT_Done_Glyph` on the `glyph` variable. That variable is not initialized before the first measurement loop, and in the render loop it is not reset to NULL after each glyph is freed. A malformed font loaded from untrusted bytes can force the load error and reach this free. This is a latent memory-safety defect; whether it crashes depends on the value in the uninitialized or stale pointer. ### Details `glyph` is declared without a NULL initializer: - `src/_imagingft.c:848` The first measurement loop can jump to `glyph_error` before `glyph` is ever assigned: - `src/_imagingft.c:1010-1013` In the render loop the glyph is freed at the end of each iteration and not set back to NULL: - `src/_imagingft.c:1242` The cleanup frees it whenever a stroker exists: - `src/_imagingft.c:1253-1256` `ImageFont.truetype` accepts a file object or bytes, so the font is attacker-suppliable. ### PoC This needs `fontTools` and any base TTF (the example uses one bundled with Pillow's tests). It rewrites glyph "A" to c
03 / Response
What to do next
- investigate
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04 / Limits
What this report cannot establish
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05 / Provenance
Sources you can inspect
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- GHSA-j4m9-6w36-pw47 ↗
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- Revision 1 ·
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