CVE-2026-66758 is an integer overflow vulnerability in the GIMP file-fits plugin. The plugin calculates memory allocation sizes using signed 32-bit integers for image width and height. If a crafted FITS image sets these values large enough, their product exceeds the 32-bit integer limit, causing an integer overflow and resulting in an undersized heap buffer allocation. Subsequently, when the cfitsio library writes a full row of pixels, it causes a heap-based buffer overflow, leading to memory corruption. This can potentially allow arbitrary code execution or denial of service. Exploitation requires local user interaction to open a malicious FITS file. Red Hat's advisory notes that default security mitigations such as SELinux enforcement, ASLR, and NX stack protection increase exploitation difficulty. Red Hat has released a security update for GIMP in Red Hat Enterprise Linux 9 to address this vulnerability.

Successful exploitation can lead to memory corruption resulting in arbitrary code execution or denial of service. However, exploitation requires user interaction by opening a crafted FITS image file. Default security mechanisms like SELinux, ASLR, and NX stack protection reduce the risk of arbitrary code execution. The vulnerability affects confidentiality, integrity, and availability of the affected system.

A security update fixing this vulnerability is available in Red Hat Enterprise Linux 9 (e.g., gimp-3.0.4-4.el9_8.9). Users should apply this update promptly. Until patched, avoid opening FITS image files from untrusted sources with GIMP to mitigate risk.