CVE-2026-30883: Heap-based Buffer Overflow in ImageMagick PNG Encoder

ImageMagick is a widely deployed open-source software suite used for image manipulation and conversion. Applications frequently utilize it as a background service to process user-uploaded images. This widespread integration makes vulnerabilities within its parsing and encoding modules highly relevant to enterprise and web application security architectures.

CVE-2026-30883 identifies a heap-based buffer overflow within the PNG encoder, specifically located in the coders/png.c component. The vulnerability is classified under CWE-119, representing an improper restriction of operations within the bounds of a memory buffer. This issue manifests when the software encounters an extremely large image profile during the encoding phase.

The vulnerability is rated with a CVSS v3.1 score of 5.7, reflecting a local attack vector with high attack complexity. Although the vector is designated as local, web applications processing untrusted user uploads typically satisfy the conditions for exploitation. The primary risk is an application crash leading to a denial of service, with secondary risks involving minor integrity impacts via heap corruption.

The core of the vulnerability lies in how the ImageMagick PNG encoder allocates and manages memory for image metadata profiles. These profiles, which include ICC color profiles, EXIF data, and XMP metadata, are embedded within the image file structure. When the encoder prepares to write or process a PNG file, it must extract and allocate memory for these profiles.

The vulnerability occurs due to insufficient bounds checking on the size of the incoming image profile before copying it into the destination heap buffer. If an image contains a malformed profile that declares a size exceeding the allocated buffer capacity, the subsequent memory copy operation writes past the buffer boundary. This action corrupts adjacent heap metadata or other application data structures.

The failure to validate the profile length against the buffer's capacity violates safe memory management principles. Because the profile size is attacker-controlled via the crafted image file, the attacker dictates the extent of the heap overflow. The exact nature of the memory corruption depends on the layout of the heap at the time the vulnerable code executes.

The vulnerable logic resides in the coders/png.c file of the ImageMagick source tree. When an image is passed to the PNG encoder, the function responsible for writing PNG chunks parses the attached profiles. Prior to the patch, the code allocated a buffer based on an expected maximum size or an improperly validated length field extracted directly from the image structure.

// Conceptual representation of vulnerable logic
size_t profile_length = GetImageProfileLength(image, "icc");
unsigned char *profile_data = (unsigned char *) AcquireQuantumMemory(expected_size, sizeof(unsigned char));
// Missing bounds check here
(void) memcpy(profile_data, GetImageProfileData(image, "icc"), profile_length);

The patch introduces strict validation against the maximum allowable profile size before proceeding with the memory allocation and copy operations. By verifying that profile_length does not exceed safe thresholds or the specifically allocated expected_size, the encoder prevents the buffer overflow.

// Conceptual representation of patched logic
size_t profile_length = GetImageProfileLength(image, "icc");
if (profile_length > MAXIMUM_PROFILE_SIZE || profile_length > expected_size) {
    ThrowWriterException(CorruptImageError, "Invalid profile length");
}
unsigned char *profile_data = (unsigned char *) AcquireQuantumMemory(profile_length, sizeof(unsigned char));
(void) memcpy(profile_data, GetImageProfileData(image, "icc"), profile_length);

This remediation ensures that the memory copy operation is strictly bounded by the validated allocation size. It removes the condition where an attacker-controlled length field can dictate a copy operation larger than the destination buffer.

Exploitation requires the delivery of a specially crafted image file to the target system. The attacker constructs a valid image file and embeds an ICC or EXIF profile with an artificially inflated size payload. The payload is designed to overflow the target buffer with specific bytes aimed at overwriting adjacent heap structures.

Once the file is delivered, the target application must process the image using ImageMagick's PNG encoder. This commonly occurs during image format conversion, resizing, or thumbnail generation tasks. The high attack complexity (AC:H) specified in the CVSS vector reflects the requirement that the target application must invoke the specific vulnerable code path within coders/png.c.

Successful exploitation results in the corruption of the heap. In a standard denial-of-service attack, overwriting heap metadata causes the memory allocator to abort the process when the corrupted chunk is subsequently freed or allocated. Achieving reliable code execution from this state requires precise manipulation of the heap layout, which is highly dependent on the host operating system and application environment.

The primary impact of CVE-2026-30883 is a denial of service. When the heap buffer overflow triggers a crash, the operating system terminates the ImageMagick process. In an application server context, continuous submission of the crafted image can lead to resource exhaustion or sustained service unavailability as worker processes are repeatedly crashed.

The CVSS v3.1 vector assesses the availability impact as High and the integrity impact as Low. The low integrity impact reflects the potential for the overflow to alter data in adjacent memory regions without necessarily achieving full arbitrary code execution. Confidentiality remains unaffected, as the vulnerability does not provide a mechanism to read or exfiltrate memory contents.

The Exploit Prediction Scoring System (EPSS) assigns this vulnerability a score of 0.00013, placing it in the 2.04th percentile. This indicates a minimal probability of observed exploitation in the wild within the near term. The specialized nature of the heap layout requirements deters widespread weaponization by threat actors.

The vendor has released patches across all actively maintained branches of ImageMagick and associated wrapper libraries. Organizations utilizing ImageMagick 7.x must upgrade to version 7.1.2-16 or later. Those on the legacy 6.x branch must deploy version 6.9.13-41 to resolve the vulnerability.

Applications relying on the Magick.NET library are also affected due to its underlying reliance on the ImageMagick core. Developers using Magick.NET should update their dependencies to version 14.10.4 or later. Dependency trees should be audited to ensure no transitive dependencies are pulling vulnerable versions into the build pipeline.

If immediate patching is unfeasible, administrators can implement temporary mitigations by configuring ImageMagick policies. The policy.xml configuration file can be modified to restrict the processing of specific image formats or to impose strict limits on memory allocation. Patching remains the only definitive resolution for this vulnerability.