CVE-2026-114501 in Pillow
Summary
by MITRE • 10/21/2026
Pillow is a Python imaging library. From 11.2.1 until 13.0.0, Arrow export assumes that an image's rows are tightly contiguous and exports from im->blocks[0].ptr even when PILLOW_ALIGNMENT makes aligned_linesize include row padding or an aligned offset before the first row. The resulting Arrow buffer can include uninitialized padding, bytes preceding the first row, or stale heap contents from previously freed images. Applications that configure alignment and export images to Arrow can therefore disclose one user's pixels or other process memory to another user. This issue is fixed in version 13.0.0.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified within the Pillow imaging library, specifically affecting versions from 11.2.1 through 13.0.0, represents a critical information disclosure flaw rooted in memory management and buffer handling during data serialization operations. The core technical issue arises when exporting images to the Apache Arrow format using the Arrow export functionality. This module incorrectly assumes that image rows are tightly contiguous in memory without accounting for alignment padding or offsets introduced by specific configuration settings such as PILLOW_ALIGNMENT. In environments where aligned line sizes include row padding or an aligned offset before the first row, the exporter fails to adjust its pointer arithmetic accordingly. Instead of calculating the correct start address based on these alignment requirements, the code directly accesses im->blocks[0].ptr, which points to the beginning of the allocated memory block rather than the actual start of the valid image data.
This miscalculation results in the inclusion of uninitialized padding bytes, memory preceding the first row, or stale heap contents from previously freed images into the exported Arrow buffer. Because the export process does not filter out these non-image regions, sensitive information residing in those memory areas is inadvertently included in the output stream. In a multi-user environment where Pillow is used to process and serialize image data for different users, this flaw allows one user's request to potentially expose pixel data or other process memory belonging to another user. The severity of this issue lies in its potential to facilitate unauthorized access to confidential information, effectively turning an internal library function into a vector for cross-user data leakage.
From a classification perspective, this vulnerability aligns with CWE-200: Exposure of Sensitive Information to an Unauthorized Actor and CWE-134: Use of Externally-Controlled Format String or similar memory exposure flaws where improper bounds checking leads to reading beyond intended buffers. In the context of the MITRE ATT&CK framework, this behavior is consistent with techniques related to Tactic 10 (Collection) under sub-techniques involving data from local system sources, specifically how an application might inadvertently collect and exfiltrate memory contents due to improper input validation or buffer handling. The flaw does not involve a traditional injection attack but rather a logic error in pointer arithmetic that leads to out-of-bounds reads during the serialization process.
The operational impact of this vulnerability is significant for any service relying on Pillow to convert images into Arrow format, particularly in data science pipelines, machine learning preprocessing steps, or web applications where image uploads are processed and stored in columnar formats like Apache Parquet or Arrow. Attackers who can trigger repeated exports with specific alignment configurations may be able to reconstruct sensitive data from the memory leaks over time. This could include proprietary images, personally identifiable information contained within user-uploaded photos, or even cryptographic keys if they reside in adjacent heap memory at the moment of export. The lack of proper boundary checks means that the vulnerability is exploitable simply by triggering the affected code path with aligned image configurations, requiring no complex exploitation steps beyond controlling the input parameters to force alignment padding.
Mitigation for this issue requires immediate upgrading to Pillow version 13.0.0 or later, where the Arrow export logic has been corrected to properly account for PILLOW_ALIGNMENT settings and calculate the correct starting pointer address. For organizations unable to upgrade immediately due to dependency constraints, implementing a temporary workaround involves avoiding the use of the Arrow export functionality with images that utilize alignment padding until an update can be applied. Additionally, developers should review any custom image processing pipelines to ensure that memory buffers are properly initialized and zeroed before reuse, although this is not a substitute for fixing the root cause in the library itself. Security teams should also monitor logs for unusual patterns of Arrow export requests from single users or services, as these could indicate attempted exploitation of the vulnerability. Regular patch management and dependency auditing remain essential practices to prevent exposure to such memory safety issues in widely used open-source libraries.