External risk intelligence

Pillow TIFF Heap Overflow Vulnerability Affects Compressed Data Handling.

CVE advisorySeverity: CRITICAL (CVSS 9.2)

CVE-2026-112393

Pillow is a general-purpose image processing library used as a dependency in many applications. While it is often used in web applications that process user-uploaded images, it is not an internet-facing service itself. Reachability depends on whether an application incorporates Pillow to process untrusted files from the internet, which is common but not inherent to the library's deployment.

Buffer Overflow

Halo Surface Signal: 3 out of 5 — possibly public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability exists in the Pillow imaging library that could lead to application crashes or potential code execution when processing specific TIFF image files. This issue arises from how the library handles compressed TIFF data, particularly when writing to memory buffers rather than actual files.

The library has a flaw when processing certain image files.
It could impact applications processing user-uploaded images.
Confirm relevance and exposure for affected systems.

Attack Path

How an attacker could exploit the issue

An attacker could send a specially crafted TIFF file to an application that uses the Pillow library to process images. If the application attempts to save this malicious file using a non-file-based target like BytesIO, the vulnerability could be triggered, potentially leading to a crash or code execution.

Malicious file sent to application.
Saving compressed TIFF data.
Process crash or code execution.

Live Threat

Current exploitation, exposure, and threat context

When Pillow is used to save compressed TIFF data to memory buffers, a heap buffer overflow and stale heap data disclosure could occur. This may happen when processing a specially crafted TIFF tag or retained ICC profile, provided the target for saving does not have a usable file descriptor. File paths and targets with real file descriptors are unaffected.

In-memory TIFF data could be corrupted.
Malicious data could trigger overflow.
Process crash or code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

The primary responsibility for addressing this vulnerability likely lies with application owners who integrate the Pillow library into their software, as they control the deployment and usage context. Infrastructure or platform teams may also be involved if Pillow is a shared dependency. The first practical step is to inventory all systems using the affected versions of Pillow, identify which instances process untrusted data, and determine their business criticality.

Application owners should own the fix.
Verify external data processing paths.
Plan for library updates or controls.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is the Pillow library?

Pillow is a widely used Python library that provides image processing capabilities. Developers integrate it into their applications to open, manipulate, and save many different image file formats. It serves as a backend component for tasks like resizing user uploads, generating thumbnails, or handling complex image data like TIFF files within software.

How does CVE-2026-112393 create a memory vulnerability?

This issue is a heap-based buffer overflow, classified as CWE-122. It happens when Pillow calculates memory space incorrectly while saving compressed TIFF data to certain in-memory objects. Because the library uses an old buffer size instead of the current position, data can be written into forbidden memory areas. This can cause the application to crash or, in some cases, allow unauthorized memory access or execution.

Does any TIFF file trigger this memory error?

No. The flaw specifically involves saving compressed TIFF data to targets that lack a standard file descriptor, such as a BytesIO stream. You are not at risk if your application only saves TIFF files directly to actual file paths on disk. The vulnerability typically requires specifically crafted image tags or retained ICC profiles to trigger the overflow, though memory leakage can occur without them.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal labels this as a 'Possible' risk. While Pillow is not an internet-facing service itself, your risk depends on whether your application uses Pillow to process untrusted images from the internet. If you host a web application that allows users to upload and process TIFF files, you should prioritize checking if those components are reachable by outside traffic.

How should I respond to this vulnerability?

Your first step is to perform an inventory to identify which of your applications depend on versions of Pillow between 2.0.0 and 13.0.0. Once identified, evaluate whether these applications handle untrusted TIFF files. The primary fix is to update the library to version 13.0.0 or later, which contains the necessary code changes to handle memory allocation correctly.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.