CVE-2026-66759: GIMP Information Disclosure Vulnerability

CVE-2026-66759 Overview

CVE-2026-66759 is an out-of-bounds read vulnerability in the file-icns plugin shipped with GIMP. The flaw resides in the icns_decompress function, which processes decompressed mask data during ICNS image parsing. The plugin reads from the mask buffer without validating that the cursor stays within the allocated resource size. A crafted ICNS file containing a truncated mask resource causes the loop to read past the buffer boundary. The result is either information disclosure, where heap memory is leaked through alpha channel pixel values, or a process crash if the read reaches unmapped memory. The weakness is classified under CWE-125.

Critical Impact
A malicious ICNS file opened in GIMP can leak heap memory contents into image pixel data or crash the application, enabling local information disclosure and denial of service.

Affected Products

GIMP file-icns plugin (ICNS image loader)
Distributions shipping the affected GIMP build, including Red Hat Enterprise Linux packages
Any application embedding the vulnerable ICNS decompression code path

Discovery Timeline

2026-07-27 - CVE-2026-66759 published to NVD
2026-07-27 - Last updated in NVD database

Technical Details for CVE-2026-66759

Vulnerability Analysis

The file-icns plugin decodes ICNS icon resources, which include a compressed mask defining the alpha channel. During processing, icns_decompress iterates over the mask data and writes decoded bytes into an output buffer. The loop uses a read cursor advanced by the compression scheme, but it does not compare the cursor position against the size of the allocated mask resource. When a crafted ICNS file declares a mask that is shorter than the decompressor expects, the routine walks past the end of the source buffer.

Because the extra bytes are written into the alpha channel of the resulting image, adjacent heap memory becomes directly observable. An attacker who can retrieve the rendered or exported image can extract residual heap data, including pointers, cryptographic material, or other sensitive content that happened to be adjacent to the mask allocation. If the out-of-bounds read touches an unmapped page, the process aborts, producing a denial of service.

Exploitation requires local file interaction: the victim must open or preview the crafted ICNS file within GIMP or an application invoking the plugin.

Root Cause

The root cause is missing bounds validation on the read cursor inside icns_decompress. The function trusts length metadata embedded in the ICNS resource and does not confirm that the cursor remains within the allocated resource size before dereferencing the source pointer. Truncated or malformed mask resources bypass this implicit assumption.

Attack Vector

The attack vector is local and requires user interaction. An attacker delivers a crafted .icns file through email, a download, a shared drive, or a project asset bundle. When the victim opens the file with GIMP, the file-icns plugin invokes icns_decompress and reads past the mask buffer. The leaked bytes appear as alpha channel pixels in the decoded image, which the attacker can recover if the victim shares the exported result or if the attacker has follow-on access.

No verified public exploit code is available for CVE-2026-66759. Technical details are tracked in the Red Hat CVE Advisory, the Red Hat Bug Report #2507557, and the upstream GNOME GIMP Issue #16528.

Detection Methods for CVE-2026-66759

Indicators of Compromise

Unexpected GIMP process crashes with SIGSEGV or SIGBUS immediately after opening an ICNS file.
ICNS files sourced from untrusted origins containing truncated or malformed mask resources.
Exported PNG or TIFF images derived from ICNS input showing anomalous or noisy alpha channel data.

Detection Strategies

Inspect ICNS files with a format validator to confirm that declared mask resource sizes match the actual compressed payload length.
Monitor endpoint telemetry for GIMP crash events (gimp-2.10, gimp-console) correlated with recently opened .icns files.
Flag execution of GIMP against files delivered by email attachments, browser downloads, or removable media.

Monitoring Recommendations

Enable core dump collection on workstations that process untrusted image assets to support forensic analysis of suspected exploitation.
Log file open events for GIMP and other consumers of the file-icns plugin using endpoint detection and response tooling.
Alert on the appearance of ICNS files in shared collaboration paths that were not present in prior baselines.

How to Mitigate CVE-2026-66759

Immediate Actions Required

Apply vendor updates for GIMP and the file-icns plugin as soon as distribution packages become available.
Instruct users to avoid opening ICNS files from untrusted sources until the patch is deployed.
Restrict GIMP execution on systems that routinely handle untrusted graphics assets, such as design review workstations.

Patch Information

Fixes are tracked upstream in GNOME GIMP Issue #16528. Distribution-specific patch status is available in the Red Hat CVE Advisory and the associated Red Hat Bug Report #2507557. Administrators should track their distribution's errata channel and apply the corresponding GIMP package update once released.

Workarounds

Disable or remove the file-icns plugin from GIMP plug-in directories to prevent automatic invocation on ICNS files.
Convert ICNS assets to safer formats such as PNG using a hardened, sandboxed conversion tool before opening them in GIMP.
Open untrusted image files inside a disposable virtual machine or container that isolates any potential heap disclosure.

bash

# Temporarily disable the vulnerable plugin by removing execute permission
chmod a-x /usr/lib64/gimp/2.0/plug-ins/file-icns/file-icns

# Verify GIMP no longer loads the plugin
gimp-console-2.10 --version