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BREW-aider-CVE-2026-112895 — Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310)

Affected: Homebrew: aider

### Summary When an application appends to an existing PDF with `Image.save(..., format="PDF", append=True)`, Pillow parses that file with `PdfParser`. Two recursive parsers have no effective bound. `linearize_page_tree` follows `/Kids` with no visited set or depth limit, so a cyclic or duplicated page tree recurses without end. `read_prev_trailer` rejects only an exactly repeated `/Prev` offset, so a long chain of unique offsets still recurses. The trailer-loop guard added for CVE-2026-42310 does not cover either case.

### Details `linearize_page_tree` recurses on `/Kids` with no cycle or depth check:

- `src/PIL/PdfParser.py:1078-1092`

`read_prev_trailer` catches only a repeated offset:

- `src/PIL/PdfParser.py:697-720` (the `processed_offsets` check at `:714-718` is the CVE-2026-42310 fix; a unique-offset chain slips past it)

### PoC ```python from PIL import PdfParser

# A page tree whose /Pages nodes reference each other in a cycle (2 -> 3 -> 2). objs = { 1: b"<< /Type /Catalog /Pages 2 0 R >>", 2: b"<< /Type /Pages /Kids [3 0 R] /Count 1 >>", 3: b"<< /Type /Pages /Kids [2 0 R] /Count 1 >>", } buf = bytearray(b"%PDF-1.4\n") off = {} for oid in (1, 2, 3): off[oid] = len(buf) buf += b"%d 0 obj\n" % oid + objs[oid] + b"\nendobj\n" xref = len(buf) buf += b"xref\n0 4\n0000000000 65535 f \n" buf += b"".join(b"%010d 00000 n \n" % off[o] for o in (1, 2, 3)) buf += b"trailer\n<< /Root 1 0 R /Size 4 >>\nstartxref\n%d\n%%%%EOF\n" % xref open("poc.pdf", "wb")…

fkie_cve-2026-112895

Pillow is a Python imaging library. From 5.1.0 until 13.0.0, Pillow can exhaust resources while parsing an existing PDF during an append operation. PdfParser follows page-tree child references without cycle or duplication tracking and follows previous-trailer chains with only an exact repeated-offset guard, so deep or cyclic page trees and long chains of unique trailer offsets can exhaust the Python stack. Repeated non-cyclic /Kids references can also cause super-linear CPU and memory use. An attacker can supply such a PDF to an application that calls Image.save with PDF append enabled. This can raise an uncaught RecursionError or consume excessive CPU and memory before output is written, causing denial of service. This issue is fixed in version 13.0.0.

GHSA-p4wg-p73j-c528 — Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310)

Affected: PyPI: pillow

### Details `linearize_page_tree` recurses on `/Kids` with no cycle or depth check:

- `src/PIL/PdfParser.py:1078-1092`

`read_prev_trailer` catches only a repeated offset:

- `src/PIL/PdfParser.py:697-720` (the `processed_offsets` check at `:714-718` is the CVE-2026-42310 fix; a unique-offset chain slips past it)

### PoC ```python from PIL import PdfParser

UBUNTU-CVE-2026-112895

Affected: Ubuntu:Pro:14.04:LTS: pillow, Ubuntu:Pro:16.04:LTS: pillow, Ubuntu:Pro:18.04:LTS: pillow, Ubuntu:Pro:20.04:LTS: pillow, Ubuntu:Pro:20.04:LTS: pillow-python2, Ubuntu:22.04:LTS: pillow, Ubuntu:24.04:LTS: pillow, Ubuntu:26.10: pillow, Ubuntu:26.04:LTS: pillow

(Pillow is a Python imaging library. From 5.1.0 until 13.0.0, Pillow ca ...)