Aider: Pillow: Memory disclosure and segfault in libtiff encoder via crafted TIFF tags (CVE-2026-112902)

The vulnerability exists in Pillow's TIFF encoder function PyImaging_LibTiffEncoderNew, where it incorrectly assumes that its own ImagingLibTiffMergeFieldInfo call overrides libtiff's internal tag field definitions. In reality, libtiff uses its built-in tag definitions to interpret variadic arguments passed to TIFFSetField(), causing a mismatch. For certain tags, such as DNGPrivateData (50740) and ActiveArea (50829), this leads to libtiff reading uninitialized or attacker-controlled arguments as pointers or counts, resulting in copying large amounts of process memory into output TIFF files or causing segmentation faults. This flaw can be triggered by opening a crafted TIFF file and saving it back as TIFF, with no special options required. The vulnerability affects multiple branches of the encoding loop and was introduced in Pillow version 5.4.0. The affected version range includes versions >=0.86.1_1 as provided. No evidence of out-of-bounds writes was found, only memory disclosure and crashes due to invalid reads.

An attacker can craft a TIFF file that, when opened and re-saved by an application using Pillow, causes the application to disclose portions of its own process memory in the output TIFF file or crash with a segmentation fault. The disclosed memory includes read-only data segments from the Pillow imaging library and potentially other linked libraries, which could aid further exploitation by defeating address space layout randomization (ASLR). The crash can cause denial of service in applications processing such images. There is no indication of arbitrary code execution or memory corruption beyond read errors and crashes.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, avoid re-saving TIFF images using Pillow when the source TIFF may be untrusted or crafted. Applications should consider disabling metadata preservation or avoid automatic routing through libtiff for TIFF saving. Monitor vendor channels for patches addressing the argument passing mismatch in the TIFF encoder. No generic mitigations are recommended beyond these specific precautions.