CVE-2026-40493: SAIL Image Library Buffer Overflow Flaw

CVE-2026-40493 Overview

CVE-2026-40493 is a critical heap buffer overflow vulnerability in the SAIL image processing library, a cross-platform library for loading and saving images with support for animation, metadata, and ICC profiles. The vulnerability exists in the PSD codec where a miscalculation between bytes-per-pixel computation and pixel buffer allocation leads to a deterministic heap buffer overflow during image processing.

Critical Impact

This vulnerability allows remote attackers to potentially achieve arbitrary code execution by crafting malicious PSD files that trigger a heap buffer overflow when processed by applications using the vulnerable SAIL library.

Affected Products

• SAIL image library versions prior to commit c930284445ea3ff94451ccd7a57c999eca3bc979
• Applications utilizing SAIL's PSD codec for LAB color mode image processing
• Systems processing untrusted PSD files with SAIL library

Discovery Timeline

• 2026-04-18 - CVE CVE-2026-40493 published to NVD
• 2026-04-20 - Last updated in NVD database

Technical Details for CVE-2026-40493

Vulnerability Analysis

The vulnerability stems from an arithmetic mismatch in the PSD codec's pixel buffer handling. When processing LAB color mode images with specific channel and depth configurations, the codec calculates bytes-per-pixel (bpp) from raw header fields using the formula (channels * depth + 7) / 8. However, the actual pixel buffer is allocated based on the resolved pixel format enumeration.

For LAB mode images with channels=3 and depth=16, the calculation yields bpp = (3*16+7)/8 = 6 bytes per pixel. However, the code incorrectly resolves this configuration to SAIL_PIXEL_FORMAT_BPP40_CIE_LAB, which only allocates 5 bytes per pixel. This 1-byte discrepancy per pixel results in every pixel write operation overshooting the allocated buffer boundary, causing a deterministic heap buffer overflow on every row of the image.

This vulnerability is classified as CWE-787 (Out-of-bounds Write), which can lead to memory corruption, denial of service, or potentially arbitrary code execution if an attacker can control the overwritten heap memory.

Root Cause

The root cause is an incorrect mapping between LAB color mode parameters and pixel format enumerations in the PSD codec's helpers.c file. When the depth is 16 bits, the code was returning SAIL_PIXEL_FORMAT_BPP40_CIE_LAB (40 bits = 5 bytes) instead of the correct SAIL_PIXEL_FORMAT_BPP48_CIE_LAB (48 bits = 6 bytes). This format mismatch causes the allocated buffer to be too small for the actual pixel data being written.

Attack Vector

An attacker can exploit this vulnerability by crafting a malicious PSD file with LAB color mode, 3 channels, and 16-bit depth. When a vulnerable application processes this file using the SAIL library, the heap buffer overflow occurs deterministically during pixel data parsing. Since the vulnerability is network-exploitable with no authentication or user interaction required, it can be triggered through any application that processes untrusted PSD images.

// Vulnerable code in src/sail-codecs/psd/helpers.c
            switch (depth)
            {
            case 8: *result = SAIL_PIXEL_FORMAT_BPP24_CIE_LAB; return SAIL_OK;
-            case 16: *result = SAIL_PIXEL_FORMAT_BPP40_CIE_LAB; return SAIL_OK;
+            case 16: *result = SAIL_PIXEL_FORMAT_BPP48_CIE_LAB; return SAIL_OK;
            }
            break;
        }

Source: GitHub Commit Details

Detection Methods for CVE-2026-40493

Indicators of Compromise

• Unexpected application crashes when processing PSD files, particularly those with LAB color mode
• Memory corruption errors or segmentation faults in applications using SAIL library
• Unusual heap memory patterns indicating buffer overflow exploitation attempts

Detection Strategies

• Monitor for crashes in applications using SAIL library during PSD file processing
• Implement file integrity monitoring for PSD files entering trusted environments
• Deploy memory protection mechanisms (ASLR, DEP) to detect exploitation attempts
• Use AddressSanitizer or similar tools during development to catch heap overflows

Monitoring Recommendations

• Enable crash dump collection for applications processing image files
• Implement logging for image processing operations, particularly for LAB mode PSD files
• Deploy endpoint detection solutions capable of identifying heap overflow exploitation patterns

How to Mitigate CVE-2026-40493

Immediate Actions Required

• Update the SAIL library to a version containing commit c930284445ea3ff94451ccd7a57c999eca3bc979 or later
• Audit applications in your environment that use the SAIL library for PSD processing
• Consider temporarily disabling PSD file processing if immediate patching is not feasible
• Implement input validation to filter or quarantine untrusted PSD files

Patch Information

The vulnerability has been patched in commit c930284445ea3ff94451ccd7a57c999eca3bc979. The fix adds proper support for BPP48_CIE_LAB pixel format and corrects the format mapping for 16-bit LAB mode images. Organizations should update to a version of SAIL that includes this commit. For detailed patch information, refer to the GitHub Security Advisory GHSA-rcqx-gc76-r9mv.

Workarounds

• Restrict processing of PSD files from untrusted sources until the patch is applied
• Implement sandboxing for image processing operations to limit the impact of exploitation
• Use alternative image processing libraries for PSD files if patching is delayed
• Deploy web application firewalls or content filters to block malicious PSD uploads

# Verify SAIL library version contains the security fix
cd /path/to/sail
git log --oneline | grep c930284445ea3ff94451ccd7a57c999eca3bc979
# If the commit is present, your version is patched