gdk-pixbuf CVE-2026-16768

The vulnerability is triggered specifically when gdk-pixbuf parses an ICO file that uses palette-based (indexed color) encoding and contains pixel index values exceeding the defined palette array length - this is the precise triggering condition. For heap content to be disclosed, the attacker must be able to supply the crafted ICO file as input to the parsing routine AND receive the rendered output image (e.g., a returned thumbnail or exported image file); services that process ICO files but do not return or expose any rendered output to the caller are not exploitable for information disclosure despite the OOB read occurring. Per CVSS PR:N, no authentication is required; per CVSS UI:N, no user interaction is required for automated server-side pipelines. Exploitation is limited by: (1) the indirect encoding of heap data as RGB pixel values requiring attacker-controlled decode; (2) the attacker needing access to the rendered output; and (3) only the partial heap region adjacent to the palette buffer being readable per crafted overflow, not arbitrary memory.

The CVSS 3.1 score of 5.3 Medium (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N) correctly reflects a remotely reachable, zero-complexity trigger with limited confidentiality impact and no integrity or availability consequence. The network attack vector is realistic for server-side pipelines - file hosting services, email gateways, and web applications commonly invoke gdk-pixbuf for automated thumbnail generation without user interaction. However, exploitation yield is constrained: heap bytes are not returned as a direct memory dump but are encoded as RGB pixel values within the output image, requiring the attacker to control input, receive output, and decode the pixel stream to recover heap content. No EPSS score was provided in available intelligence. KEV status is absent (not confirmed in CISA KEV), and no public POC has been identified, suggesting this has not yet been opportunistically weaponized. The realistic risk is moderate for organizations running image-processing pipelines exposed to untrusted ICO files with output returned to callers; it is negligible for environments where image output is discarded or not accessible to the submitter.

An attacker submits a crafted ICO file - with palette-indexed pixel entries whose index values exceed the palette array size - to a web application that uses gdk-pixbuf to generate and return a thumbnail preview. The library reads beyond the palette boundary into heap memory, and those bytes are rendered as RGB pixel values in the returned thumbnail image. The attacker downloads the thumbnail and decodes pixel RGB values to reconstruct contiguous heap content, potentially recovering sensitive data such as heap pointers, session tokens, or cryptographic material resident in the process address space.