CVE-2026-112405 in Pillow
Summary
by MITRE • 10/20/2026
Pillow is a Python imaging library. From 12.0.0 until 13.0.0, Pillow's Image.merge() can dereference a null image8 plane. Validation skips the first input band, allowing a 32-bit integer or floating-point image backed by image32 storage to be merged as a narrower multiband image. A crafted IPTC file can reach this path when an application opens and loads it, or a caller can invoke Image.merge() directly with such a first band. This causes a native process crash. This issue is fixed in version 13.0.0.
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Analysis
by VulDB Data Team • 10/20/2026
The vulnerability identified within the Pillow Python imaging library affects versions ranging from 12.0.0 through 13.0.0, specifically targeting the Image.merge() function which is responsible for combining multiple image bands into a single composite image. This flaw stems from an insufficient validation mechanism during the processing of input data streams, particularly when handling multiband images that utilize specific internal storage formats such as image8 or image32. The core technical deficiency lies in how the library validates and processes the first band of input data before merging it with subsequent bands. In a properly secured implementation, every input channel must undergo rigorous type checking and boundary validation to ensure compatibility with the target output format. However, in this vulnerable version, the validation logic erroneously skips checks on the initial input band, creating a pathway for malformed or crafted inputs to bypass security controls that would otherwise prevent unsafe memory operations.
The operational impact of this flaw is significant because it allows an attacker to trigger a null pointer dereference within the native C backend of Pillow. When a user opens and loads a specially crafted IPTC file, or when a developer directly invokes Image.merge() with a first band configured as a 32-bit integer or floating-point image backed by image32 storage but intended for merging into a narrower multiband structure like an eight-bit image, the library fails to detect the incompatibility. Instead of raising an appropriate exception or rejecting the input, the code proceeds to dereference memory addresses associated with null pointers in the image8 plane. This results in an immediate crash of the native process running Pillow, leading to a denial of service condition for any application relying on this functionality. The severity is compounded by the fact that IPTC files are commonly used in photography and media workflows, increasing the likelihood of exposure if such files originate from untrusted sources or user uploads.
From a classification perspective, this vulnerability aligns with CWE-476, which denotes NULL Pointer Dereference, as the root cause involves accessing memory through an invalid pointer due to inadequate input validation. It also relates closely to CWE-20, Improper Input Validation, since the failure stems from skipping necessary checks on the first band of data during the merge operation. In terms of adversarial tactics, this could be leveraged within ATT&CK technique T1499, Endpoint Denial of Service, where an attacker aims to disrupt availability by causing application crashes through crafted inputs. The attack vector is primarily local or network-based depending on whether the vulnerable code processes user-uploaded files in a web service context or handles data from external APIs.
Mitigation strategies for this vulnerability are straightforward and center around immediate software updates. Organizations and developers using Pillow must upgrade to version 13.0.0 or later, where the validation logic has been corrected to properly inspect all input bands regardless of their position in the sequence. For environments that cannot immediately patch due to dependency constraints, implementing strict input sanitization at the application layer is recommended. This includes validating image formats and dimensions before passing them to Pillow functions, as well as employing try-except blocks around Image.merge() calls to gracefully handle potential exceptions rather than allowing uncaught crashes to terminate processes. Additionally, deploying runtime protection mechanisms such as memory safety wrappers or sandboxing can help contain the impact of any remaining exploitable instances in legacy systems until full migration is complete.