SAIL Library PSD Codec Heap Buffer Overflow Vulnerability (CVE-2026-40493)

SAIL (Simple API for Images Loading) is a cross-platform library used for loading and saving images, supporting features like animation, metadata handling, and ICC profiles. A critical vulnerability, CVE-2026-40493, has been identified within the PSD codec of SAIL. This flaw stems from an inconsistency in how the library calculates bytes per pixel (bpp) compared to the actual memory allocated for pixel data. Specifically, when processing images in LAB mode with channels=3 and depth=16, the computed bpp value doesn't align with the memory allocated by the BPP40_CIE_LAB format, resulting in a heap buffer overflow during pixel write operations. The vulnerability affects versions prior to commit c930284445ea3ff94451ccd7a57c999eca3bc979, which contains the necessary patch to resolve this issue. Successful exploitation could lead to arbitrary code execution.

Attack Chain

1. An attacker crafts a malicious PSD image specifically designed to trigger the vulnerability. This image is created with LAB color mode, 3 channels, and a depth of 16 bits per channel.
2. The victim application utilizes the SAIL library to load the crafted PSD image. This could be a photo editor, image viewer, or any other software incorporating SAIL for image processing.
3. The PSD codec within SAIL calculates the bpp value based on the channels and depth header fields. In this specific case, the calculation results in a bpp value of 6.
4. The pixel buffer is allocated based on the resolved pixel format, BPP40_CIE_LAB, which allocates only 5 bytes per pixel.
5. During pixel writing, the code attempts to write 6 bytes of data into a buffer allocated for only 5 bytes, resulting in a one-byte heap buffer overflow. This overflow occurs deterministically on every row of the image.
6. The heap buffer overflow corrupts adjacent memory regions on the heap.
7. Depending on the overwritten data, the attacker could potentially gain control of program execution by overwriting function pointers or other critical data structures.
8. The attacker achieves arbitrary code execution on the victim's machine, leading to system compromise.

Impact

Successful exploitation of CVE-2026-40493 allows an attacker to achieve arbitrary code execution on a vulnerable system. This could lead to complete system compromise, data exfiltration, or denial-of-service. Applications that rely on the SAIL library to process PSD images are at risk. The vulnerability's high CVSS score (9.8) indicates its critical severity and potential for widespread impact. The number of affected systems depends on the adoption rate of the SAIL library in various software applications across different sectors.

Recommendation

• Upgrade to a version of SAIL that includes commit c930284445ea3ff94451ccd7a57c999eca3bc979 or later to patch CVE-2026-40493.
• Monitor applications that use the SAIL library for unexpected crashes or anomalous behavior, which could indicate exploitation attempts. Enable process creation logging (Sysmon on Windows) to activate the rule detecting abnormal processes spawned by image processing applications.
• Deploy the Sigma rule Detect SAIL PSD Heap Overflow to identify potential exploitation attempts based on process creation events.