CVE-2026-25990: 
Python vulnerability analysis and mitigation

CVE-2026-25990 is an out-of-bounds write vulnerability in Pillow, the Python imaging library, triggered when loading a specially crafted PSD (Photoshop Document) image. It affects Pillow versions 10.3.0 through 12.1.0 (i.e., >= 10.3.0, < 12.1.1) and was disclosed and patched on February 11, 2026. The vulnerability carries a CVSS v3.1 base score of 7.5 (High) and a CVSS v4.0 base score of 8.6 (High) (GitHub Advisory, Openwall).

The root cause is an out-of-bounds write (CWE-787) in Pillow's image tile decoding and encoding logic in src/decode.c and src/encode.c. Specifically, the _setimage function failed to validate that tile x and y offsets were non-negative before processing, allowing a specially crafted PSD file with invalid (negative) tile extents to trigger a write beyond the intended buffer boundary. The fix adds explicit checks for negative xoff and yoff values, raising a ValueError if tile extents are invalid rather than proceeding with the out-of-bounds write (GitHub Commit, GitHub Advisory). Exploitation requires that an attacker supply a malicious PSD file to an application that processes it using a vulnerable Pillow version.

Successful exploitation can cause a denial of service by crashing the application processing the malicious PSD image. The CVSS v4.0 scoring also indicates potential high impact on confidentiality and integrity of the vulnerable system, suggesting that in certain scenarios the out-of-bounds write could be leveraged beyond a crash. Downstream products incorporating Pillow are also affected, including multiple IBM products (Maximo Application Suite, Cloud Pak for Automation, IBM Instana, IBM Guardium Data Security Center, watsonx Orchestrate, and others) as well as Oracle products (GitHub Advisory, Red Hat Bugzilla).

As of the time of reporting, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (Feedly). The EPSS score is approximately 0.015% (3rd percentile), indicating a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported.

1. Craft a malicious PSD file: Create a PSD image file with invalid tile extents — specifically, tile x or y offsets set to negative values — that will trigger the out-of-bounds write when parsed by Pillow's decoder.
2. Deliver the file to the target: Submit the crafted PSD file to any application or service that uses a vulnerable Pillow version (>= 10.3.0, < 12.1.1) to open or process image files (e.g., via file upload, API endpoint, or email attachment processing).
3. Trigger image loading: The application calls Image.open() on the malicious PSD file, which invokes the vulnerable _setimage function in decode.c without validating negative tile offsets.
4. Out-of-bounds write occurs: The decoder writes image data past the intended buffer boundary, potentially causing an application crash (denial of service) or, in more complex scenarios, memory corruption (GitHub Commit, GitHub Advisory).

• Logs: Application crash logs or Python tracebacks referencing Pillow's PSD image processing, particularly errors in PsdImagePlugin or ImageFile modules; unexpected ValueError or SystemError exceptions related to tile extents.
• File System: Presence of unexpected or suspicious .psd files in upload directories or temporary processing folders.
• Process: Abnormal termination or segmentation faults in Python processes that handle image uploads or processing; repeated crashes of image-processing worker processes.

Upgrade Pillow to version 12.1.1 or later, which contains the fix for this vulnerability (GitHub Advisory, Openwall). As a workaround where immediate patching is not possible, use the formats parameter of Image.open() to explicitly exclude PSD from the list of accepted formats, preventing malicious PSD files from being processed. Additionally, restrict file upload capabilities to trusted sources, implement input validation to reject PSD files if not required, and monitor for unexpected application crashes during image processing. Red Hat has issued errata (RHSA-2026:3462, RHSA-2026:4128, RHSA-2026:6277, RHSA-2026:14873, RHSA-2026:14874, RHSA-2026:6277) for affected products (Red Hat Bugzilla).

The vulnerability was reported by security researcher Yarden Porat and remediated by the Pillow maintainers (radarhere, wiredfool, hugovk). The disclosure was coordinated through GitHub's security advisory process and announced on the oss-security mailing list by Alan Coopersmith of Oracle Solaris Engineering (Openwall). Multiple Linux distributions (Ubuntu, Fedora, Debian, SUSE, Amazon Linux) and enterprise vendors (IBM, Oracle, Red Hat, Splunk) issued advisories and patches for affected downstream products, reflecting broad ecosystem impact.