GIMP: RCE Flaw in PSP Files Discovered, Update Available

On September 9, 2026, Trend Micro published advisory ZDI-26-633, documenting a vulnerability in GIMP's parsing of the PSP file format that enables remote code execution. The initial vendor notification dates back to April 17: a window of nearly five months during which the open-source project had time to prepare and release a fix before coordinated disclosure. The case reignites the debate over the risks of supporting legacy proprietary formats in widely distributed graphics software, where parsing third-party files represents an often underestimated attack surface.

The Mechanism: From Integer Overflow to Code Execution

The specific flaw resides in the PSP file parsing routine, a proprietary format originally developed by Jasc Software for Paint Shop Pro and later maintained by Corel. According to the ZDI advisory, the defect stems from the failure to validate user-supplied data, which can trigger an integer overflow prior to buffer allocation. The CVE-2026-4153 record, published by MITRE, describes the operational result as a heap-based buffer overflow: copying data into an undersized buffer allows overwriting of memory control structures.

The two descriptions are technically compatible. The arithmetic integer overflow alters the requested allocation size; the subsequent copy of user data into the too-small buffer produces the actual overflow. This chain of events is typical of complex file format parsing, where attacker-manipulated length or offset fields are not subjected to sanity checks before use.

Code execution occurs in the context of the current GIMP process. No authentication is required (PR:N, Privileges Required: None), but user interaction is necessary (UI:R, User Interaction: Required): the target must visit a malicious page or open a specially crafted PSP file. The local attack vector (AV:L) indicates that initial access typically occurs through the local filesystem, not via a remote network.

"This vulnerability allows remote attackers to execute arbitrary code on affected installations of GIMP. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file." — Advisory ZDI-26-633

Why Legacy Formats Remain a Critical Attack Surface

GIMP supports dozens of file formats, both native and third-party. The PSP format falls into the latter category: a historical proprietary format whose full specification is not always public or up to date. This scenario recurs across the graphics software ecosystem: open-source applications must implement parsers for commercial formats to ensure interoperability, but the quality of reverse engineering and the frequency of security audits on these modules tend to be lower than for core components.

The result is a risk asymmetry. A user who receives an apparently innocuous PSP file — perhaps forwarded as an email attachment or downloaded from a graphics resource — can compromise their entire workstation simply by opening it in GIMP. The nature of the vector (an image file) makes the attack particularly insidious in enterprise contexts where graphics files are routinely exchanged among designers, marketing teams, and external vendors.

The vulnerability does not affect GIMP's native XCF format, but exclusively the PSP parser. This granularity is relevant for risk assessment: workflows that do not involve importing Paint Shop Pro files are theoretically exposed only if a user deliberately opens a file in that format.

Coordinated Disclosure and the Vendor Fix

The timeline documented by ZDI shows a classic responsible disclosure process. The initial vendor notification is dated April 17, 2026; coordinated public release occurred on September 9, 2026. During this period, GIMP was able to develop and distribute a correction. The ZDI advisory explicitly confirms: "GIMP has issued an update to correct this vulnerability".

The CVE record cites the internal ZDI reference ZDI-CAN-28874, formally linking the two sources. The CVSS 7.8 assigned by MITRE places the vulnerability in the high-severity band: confidentiality, integrity, and availability are all rated with "High" impact (C:H/I:H/A:H). The full CVSS vector CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H quantifies the attack profile: low complexity, no privileges required, but human action is necessary.

The sources do not reveal the patched GIMP version nor technical details of the commit or patch. A link to a vendor advisory on gitlab.gnome.org is referenced in the CVE record but is not externally verifiable. The specific affected versions are not stated in the available dossier.

Recommended Actions

The combination of CVSS 7.8, a file-based vector, and the availability of a fix makes this vulnerability a priority for environments running GIMP in production. Actions indicated by the technical context and sources:

• Verify and apply the GIMP update released before September 9, 2026, to installations exposed to PSP file workflows.
• Scrutinize the origin of incoming PSP files: the required user interaction means controlling the file distribution chain drastically reduces the attack surface.
• Isolate graphics workstations where GIMP processes files from untrusted sources, limiting the blast radius of a potential compromise.
• Review format import policies: if the PSP format is not required for business workflows, consider disabling it or opening such files only in sandboxed environments.

Why This Flaw Fits a Broader Pattern

CVE-2026-4153 is not an isolated case, but the latest link in a chain tying mature software to risks in parsing legacy formats. Active since 1996, GIMP has accumulated support for dozens of proprietary formats over two and a half decades. Every added parser expands the attack surface; not all receive the same scrutiny from security researchers or core contributors.

The case illustrates how backward compatibility is often in tension with security. Maintaining PSP support ensures continuity for users migrating from Paint Shop Pro, but imposes a maintenance and verification burden that resource-constrained open-source projects struggle to sustain. ZDI's coordinated disclosure, with its nearly five-month window, allowed the project to close the gap before publication; residual risk now hinges on the speed of update adoption by users.

No in-the-wild exploits or details on usable shellcode techniques are documented. The absence of this information in the sources does not rule out undetected activity, but the dossier provides no evidence to that effect. The identity of the researcher who discovered the vulnerability is not mentioned in advisory ZDI-26-633.

Sources

• http://www.zerodayinitiative.com/advisories/ZDI-26-633/
• https://www.cve.org/CVERecord?id=CVE-2026-4153
• http://www.zerodayinitiative.com/advisories/upcoming/
• https://www.trendmicro.com/
• https://www.trendmicro.com/en_us/business/products/one-platform.html

Information verified against cited sources and current as of publication.

Sources