CVE-2026-66758 Overview
CVE-2026-66758 is an integer overflow vulnerability [CWE-190] in the file-fits plugin bundled with the GNU Image Manipulation Program (GIMP). The plugin calculates memory allocation sizes for Flexible Image Transport System (FITS) images using signed 32-bit integers for width and height. A crafted FITS file that sets both dimensions to large values causes their product to exceed 2^31 and overflow, producing an undersized heap allocation. The cfitsio library then writes a full row of pixels into that buffer, triggering a heap-based buffer overflow. Successful exploitation can lead to arbitrary code execution or a denial-of-service condition in the context of the user running GIMP.
Critical Impact
A user who opens a malicious FITS file in GIMP can experience memory corruption that may result in arbitrary code execution under their user account.
Affected Products
- GIMP file-fits plugin (FITS image loader)
- GIMP distributions bundling the vulnerable plugin as tracked in GNOME GIMP Issue #16528
- Linux distributions shipping the affected GIMP package, including advisories tracked in the Red Hat CVE-2026-66758 Advisory
Discovery Timeline
- 2026-07-27 - CVE-2026-66758 published to the National Vulnerability Database
- 2026-07-29 - Last updated in NVD database
Technical Details for CVE-2026-66758
Vulnerability Analysis
The flaw resides in the memory-sizing logic of the file-fits plugin. When GIMP opens a FITS image, the plugin reads the width and height fields from the file header and multiplies them to determine the size of the pixel buffer to allocate on the heap. Both values are handled as signed 32-bit integers. When the product exceeds INT_MAX (2^31 − 1), the arithmetic wraps around and yields a small positive value. The plugin then requests a heap buffer sized to that truncated result.
After allocation, the plugin delegates pixel decoding to cfitsio, which writes an entire row of pixel data based on the untrusted width value. Because the destination buffer is far smaller than the row cfitsio writes, adjacent heap memory is corrupted. An attacker who controls the surrounding heap layout can convert this corruption into control-flow hijacking and arbitrary code execution.
Root Cause
The root cause is missing overflow validation before allocation. The plugin trusts attacker-controlled dimensions and performs width * height * bytes_per_pixel arithmetic on signed 32-bit integers without checking for wraparound. Widening to 64-bit types, using checked-multiplication helpers, or rejecting oversized dimensions would prevent the undersized allocation.
Attack Vector
Exploitation requires local user interaction: a victim must open a crafted .fits file in GIMP. The attack vector is local and user-interaction dependent, so realistic delivery paths include phishing attachments, malicious downloads, and shared image archives. No elevated privileges are required to trigger the flaw; the resulting code execution runs with the privileges of the GIMP process. See the Red Hat Bug Report #2507475 for additional detail.
No verified public proof-of-concept code is available at time of writing. The bug is described in prose only; readers should consult the GNOME GIMP Issue #16528 tracker for source-level context.
Detection Methods for CVE-2026-66758
Indicators of Compromise
- FITS image files (.fits, .fit, .fts) with header NAXIS1 or NAXIS2 values large enough that their product exceeds 2^31.
- GIMP process crashes or SIGSEGV events immediately after opening a FITS file.
- Unexpected child processes or shell invocations spawned by the GIMP process shortly after image import.
Detection Strategies
- Inspect FITS file headers at email and file-sharing gateways and flag files whose declared dimensions produce a 32-bit integer overflow.
- Enable heap protections such as glibc MALLOC_CHECK_ or AddressSanitizer in test environments to surface the corruption during triage.
- Correlate GIMP crash telemetry with recent file-open events to identify targeted user interaction.
Monitoring Recommendations
- Monitor endpoints for GIMP child processes that deviate from normal image-editing workflows.
- Alert on GIMP writing to or executing files outside standard user directories after opening an image.
- Ingest application crash logs into a central log platform to detect clusters of GIMP faults tied to FITS handling.
How to Mitigate CVE-2026-66758
Immediate Actions Required
- Apply vendor updates for GIMP as soon as your Linux distribution or GIMP maintainers publish patched packages tracked in the Red Hat CVE-2026-66758 Advisory.
- Advise users not to open FITS files received from untrusted or unexpected sources.
- Restrict GIMP execution on shared analyst workstations until patches are deployed.
Patch Information
At publication, the vulnerability is tracked upstream in GNOME GIMP Issue #16528 and downstream in the Red Hat CVE-2026-66758 Advisory. Consult your distribution's security channel for the fixed package version and apply it through your standard package manager. No fixed version string is available in the NVD record at this time.
Workarounds
- Remove or disable the file-fits plugin from GIMP's plugin directory if FITS support is not required in your workflow.
- Enforce file-type allowlists at endpoint and gateway controls to block inbound .fits, .fit, and .fts files.
- Run GIMP inside a sandbox such as Flatpak, Firejail, or a container to constrain the impact of successful exploitation.
# Example: disable the file-fits plugin for the current user
mv ~/.config/GIMP/*/plug-ins/file-fits ~/.config/GIMP/file-fits.disabled 2>/dev/null
# System-wide (Debian/Ubuntu path; adjust for your distribution)
sudo chmod 000 /usr/lib/gimp/*/plug-ins/file-fits
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
