CVE-2026-3707: MrNanko webp4j Buffer Overflow Vulnerability

CVE-2026-3707 Overview

An integer overflow vulnerability has been identified in MrNanko webp4j versions up to 1.3.x. The vulnerability exists in the DecodeGifFromMemory function within src/main/c/gif_decoder.c. Manipulation of the canvas_height argument can trigger an integer overflow condition, which may lead to heap buffer overflow and memory corruption. Local access is required to exploit this vulnerability.

Critical Impact

Local attackers with access to the system can exploit this integer overflow to potentially corrupt memory, cause application crashes, or achieve code execution through heap buffer overflow conditions.

Affected Products

• MrNanko webp4j versions up to 1.3.x
• Applications utilizing the webp4j GIF decoder functionality
• Systems processing GIF images through the affected library

Discovery Timeline

• 2026-03-08 - CVE-2026-3707 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3707

Vulnerability Analysis

The vulnerability resides in the GIF decoder component of the webp4j library, specifically in how the canvas_height parameter is processed. When multiplying width and height values to calculate buffer sizes or iteration counts, the code fails to account for potential integer overflow conditions. This occurs because the multiplication is performed using signed 32-bit integers (int), which can wrap around to negative or smaller-than-expected values when the product exceeds the maximum representable value.

The integer overflow subsequently leads to a heap buffer overflow condition. When the calculated size wraps around to a smaller value, the allocated buffer becomes insufficient to hold the actual data being written, causing memory corruption beyond the allocated boundaries.

Root Cause

The root cause is the use of signed integer arithmetic (int) for calculating buffer indices and sizes without proper overflow checks. In the vulnerable code path, the expression width * height is evaluated as a signed integer multiplication. For large dimension values, this multiplication can overflow, producing an incorrect (often much smaller) result. The fix addresses this by casting the operands to size_t before multiplication, ensuring the arithmetic is performed in an unsigned type with sufficient range to prevent overflow on typical platforms.

Attack Vector

This vulnerability requires local access to exploit. An attacker would need to craft a malicious GIF file with specially chosen dimension parameters designed to trigger the integer overflow when processed by the DecodeGifFromMemory function. When the vulnerable application processes this crafted image, the overflow occurs during buffer iteration, potentially allowing:

1. Memory Corruption - Writing beyond allocated buffer boundaries
2. Denial of Service - Causing application crashes through memory access violations
3. Potential Code Execution - In certain scenarios, controlled heap corruption could enable arbitrary code execution

// Vulnerable code pattern (before patch)
for (int i = 0; i < width * height; i++) {
    canvas[i * 4 + 0] = r;
    canvas[i * 4 + 1] = g;
    canvas[i * 4 + 2] = b;
    // Integer overflow in width * height can cause heap buffer overflow
}

// Fixed code (after patch)
for (size_t i = 0; i < (size_t)width * height; i++) {
    canvas[i * 4 + 0] = r;
    canvas[i * 4 + 1] = g;
    canvas[i * 4 + 2] = b;
    // Using size_t prevents integer overflow
}

Source: GitHub Commit Changes

Detection Methods for CVE-2026-3707

Indicators of Compromise

• Unexpected application crashes during GIF image processing operations
• Memory access violation errors or segmentation faults in processes using webp4j
• Anomalous GIF files with unusually large or suspicious dimension values in image headers
• Heap corruption signatures detected by memory protection mechanisms

Detection Strategies

• Implement file integrity monitoring for applications using webp4j library
• Deploy memory protection tools (ASAN, Valgrind) in development and testing environments to detect heap buffer overflows
• Monitor application logs for crashes or errors originating from GIF decoding functions
• Scan application dependencies to identify vulnerable webp4j versions (≤1.3.x)

Monitoring Recommendations

• Enable crash dump collection and analysis for applications processing image files
• Implement input validation to reject GIF files with abnormally large dimension parameters
• Configure SentinelOne to monitor for memory corruption attack patterns and exploit attempts
• Set up alerts for unusual file processing behavior or repeated application crashes

How to Mitigate CVE-2026-3707

Immediate Actions Required

• Upgrade webp4j to a patched version that includes commit 89771b201c66d15d29e4cc016d8aae82b6a5fbe1
• Review all applications that depend on webp4j and schedule updates accordingly
• Implement input validation to limit maximum GIF dimensions before processing
• Consider disabling GIF processing functionality if not required until patching is complete

Patch Information

A security patch is available that addresses the integer overflow vulnerability. The fix, identified by commit hash 89771b201c66d15d29e4cc016d8aae82b6a5fbe1, modifies the vulnerable loop to use size_t type for the iteration variable and casts the multiplication operands appropriately. This ensures the arithmetic is performed using unsigned integers with sufficient range to prevent overflow.

For detailed patch information, refer to the GitHub Commit Changes and the GitHub Issue Discussion.

Workarounds

• Implement pre-processing validation to reject GIF files with dimensions exceeding safe thresholds (e.g., width × height < 2^30)
• Use alternative image processing libraries that are not affected by this vulnerability
• Deploy application sandboxing to limit the impact of potential exploitation
• Enable compiler-level protections such as stack canaries and ASLR for applications using the vulnerable library

# Example: Validate GIF dimensions before processing
# Maximum safe dimension to prevent integer overflow
MAX_DIMENSION=65535

# Check GIF header for dimensions (simplified example)
identify -format "%w %h" input.gif | while read width height; do
    if [ "$width" -gt "$MAX_DIMENSION" ] || [ "$height" -gt "$MAX_DIMENSION" ]; then
        echo "Rejecting GIF with unsafe dimensions: ${width}x${height}"
        exit 1
    fi
done