Pillow EUVD-2026-107575

Exploitation requires a specific non-default deployment: the application must configure a non-default PILLOW_ALIGNMENT (so aligned_linesize adds row padding or an aligned offset before the first row) AND export images to the Arrow format via the __arrow_c_array__ / Arrow C interface. The leak is most pronounced for small or cropped images where per-row padding is significant, and for the information to cross trust boundaries the deployment must be multi-user (one user's export must be able to reach another user). Limiting factors: default Pillow configurations do not set custom alignment and are not affected; single-user or non-Arrow workflows cannot leak cross-tenant data; affects only versions 11.2.1 through 12.x, fixed in 13.0.0. The AT:P metric reflects that these configuration prerequisites are outside the attacker's control.

This is a genuine but narrowly-scoped information-disclosure flaw (CWE-226) that should be treated as a moderate, not top, priority. The only severity signal provided is a vendor/GitHub CVSS 4.0 vector (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N, score 6.3): network vector, no privileges or user interaction, but with AT:P (a present attack requirement) and only Low confidentiality impact and no integrity/availability impact. The AT:P flag is the key nuance - exploitation is conditional on the application enabling PILLOW_ALIGNMENT and exporting images to Arrow, so this is not a straightforward remote attack despite AV:N. There is no EPSS score, no CISA KEV listing, and no public exploit referenced in the data, so exploitation status is 'no public exploit identified at time of analysis'. No SSVC decision data was supplied. The disclosed content is uninitialized padding or stale heap from previously freed images, which can leak another user's pixels or process memory - meaningful in multi-tenant image-processing services but useless against single-user deployments. Net: a real, fix-worthy bug for multi-user services that use Pillow's Arrow export with custom alignment, but low urgency for the large majority of Pillow users who never touch alignment or Arrow export.

A multi-tenant image service built on Pillow is configured with a non-default PILLOW_ALIGNMENT and exposes image data to clients via the Arrow C array interface. When one user requests an Arrow export of a small or cropped image, the buffer sent back includes padding bytes or stale heap left over from a previously freed image belonging to another user, leaking their pixels or other process memory. No public proof-of-concept was referenced, though the fixing PR (#10172) includes regression tests that demonstrate the non-contiguous/aligned conditions.