GHSA-xg8h-j46f-w952 Pillow vulnerability can cause write buffer overflow on BCn encoding

• PyPI pillow: >= 11.2.0, < 11.3.0 → fixed in 11.3.0

There is a heap buffer overflow when writing a sufficiently large (>64k encoded with default settings) image in the DDS format due to writing into a buffer without checking for available space. This only affects users who save untrusted data as a compressed DDS image. • Unclear how large the potential write could be. It is likely limited by process segfault, so it's not necessarily deterministic. It may be practically unbounded. • Unclear if there's a restriction on the bytes that could be emitted. It's likely that the only restriction is that the bytes would be emitted in chunks of 8 or 16. This was introduced in Pillow 11.2.0 when the feature was added.