Description

A flaw was found in GIMP's ICO file loader. When processing an ICO file containing an embedded PNG image, an integer overflow can occur during the calculation of the required buffer size. This leads to an undersized buffer being allocated, causing a heap-based buffer overflow when the decoded pixel data is written. A remote attacker could exploit this by crafting a malicious ICO file, which, when opened, could lead to arbitrary code execution or a crash.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-09-14T14:17:20.693Z",
  "pubdate": "2026-09-14T14:17:20.693Z",
  "executiveSummary": "A critical security vulnerability has been identified within the GIMP ICO file loader, specifically affecting the processing of embedded PNG images. The vulnerability is classified as an integer overflow, which manifests during the calculation of memory requirements for pixel data buffers. This flaw results in the allocation of an undersized heap buffer, subsequent to which the application performs out-of-bounds write operations. The impact of this vulnerability is severe, potentially allowing a remote attacker to achieve arbitrary code execution on a victim's machine or induce a process crash. Successful exploitation requires a user to open a specially crafted, malicious ICO file. Given the nature of image processing software, this vulnerability poses a significant risk to users who may encounter untrusted media content. No specific authentication or elevated privileges are required for exploitation beyond the victim initiating the file import process, making the attack surface readily accessible to remote threats.",
  "technicalDetails": "The vulnerability resides within the GIMP ICO file parsing logic, specifically where the handler processes embedded PNG data. The root cause is an integer overflow occurring during the arithmetic operations used to determine the total memory size required for the destination pixel buffer. When the parser computes the buffer dimensions based on the dimensions and bit depth of the embedded PNG image, the resulting calculation may wrap around due to insufficient bounds checking on input parameters provided within the file structure.\nDuring the exploitation flow, the attacker crafts a malicious ICO file containing a PNG resource with dimensions or metadata that trigger this integer overflow. When GIMP attempts to allocate a heap buffer using the overflowed size value, the allocated memory block is smaller than the actual pixel data to be decoded. Subsequently, as the decoding engine decompresses and copies the pixel data into the insufficient buffer, it performs a heap-based buffer overflow. This process overwrites adjacent memory segments on the heap, allowing an attacker to corrupt critical internal structures or control flow metadata.\nThis vulnerability is triggered without the need for authentication, as it involves the parsing of untrusted file formats directly through the user-facing interface. Since the processing of image data is generally performed in the user's security context, successful exploitation grants the attacker the privileges of the GIMP process. In a successful exploitation scenario, the heap corruption can be leveraged to redirect execution flow toward shellcode or Return-Oriented Programming (ROP) gadgets, enabling arbitrary code execution. The attack is initiated remotely, as a user simply needs to load the malicious ICO image, making it an effective vector for file-based attacks. The complexity of modern heap allocators may influence the reliability of exploitation, but the inherent flaw provides a direct mechanism for memory corruption during the normal course of file processing, leading to immediate system compromise or denial-of-service via crash."
}