CVE-2026-59088

Executive Summary

CVE-2026-59088 is a signed integer overflow vulnerability (CWE-190) in the GNU Image Manipulation Program (GIMP) file-fli plugin, triggered during memory allocation for FLI image file processing. An attacker can craft a malicious FLI file with image dimensions large enough that the multiplication of width by height overflows a signed integer, resulting in insufficient memory allocation and subsequent application crash. The vulnerability requires user interaction — a victim must open the malicious file — and achieves denial of service (availability impact only) with a CVSS base score of 5.5. Any GIMP installation with the file-fli plugin enabled is affected; no patch has been identified and no public exploit code has been observed, indicating the vulnerability is currently unpatched.

Technical Analysis

Vulnerability Class: Signed Integer Overflow (CWE-190).

Affected Component: The file-fli plugin in GIMP, responsible for importing FLI animation files (an Autodesk Animator format). The NVD description states the flaw is present "when processing FLI image files" and stems from "an incorrect calculation during memory allocation for image buffers."

Mechanism: When GIMP's file-fli plugin parses an FLI file, it computes the required buffer size for image data. This calculation multiplies the image width by the image height. The NVD description explicitly states: "the multiplication of image width and height can exceed the maximum integer value." In C-based code (GIMP is written in C), signed integer overflow produces undefined behavior — in practice, on a 32-bit int (32-bit signed, max value 2,147,483,647), an overflow yields a negative or truncated value. The result is that the plugin allocates a buffer that is too small for the actual image data (or computes an erroneous offset), leading to memory corruption or an out-of-bounds operation.

Attack Surface: The attack surface is the FLI file parser. FLI files are a legacy animation format; while no longer widely used, they are still supported by GIMP. The attack vector is local-file-driven: the attacker supplies a crafted FLI file that is opened by a victim. This could be delivered via email attachment, download, or a web page prompting a file download, and then classic social engineering (e.g., "open this animated image") induces the user to open it in GIMP.

Failure Impact: The vulnerability manifests as an application crash (denial of service). The NVD description notes "leading to the application crashing and resulting in a denial of service." There is no indication of code execution or memory disclosure, based on the NVD scoring (C:N/I:N/A:H — no confidentiality or integrity impact).

Specific Code-Level Detail: The NVD description provides only the function-name-level detail that the issue is in the file-fli plugin; no specific function names within the plugin are disclosed. The multiplication of width and height is the specific arithmetic operation. No patch has been published.

Exploitation Scenarios

Note: No public PoC or exploit code has been observed. The following attack chain is inferred strictly from the vulnerability description and class (signed integer overflow leading to memory layout miscalculation).

Step 1 — Reconnaissance and Target Identification The attacker identifies a target running a GIMP installation with the FLI plugin enabled (default in most builds). Reconnaissance may involve checking for GIMP in software inventory (e.g., via user agent strings on web forums, or simply targeting a known user of the application). The attacker does not need privileged access — the vulnerability is triggered locally with user interaction.

Step 2 — Flaw Trigger The attacker crafts a malicious FLI file. The attack relies on setting the file's image dimension fields (width and height) to calculated values such that width × height exceeds the maximum positive signed 32-bit integer (2,147,483,647). For example, values on the order of 65,536 × 65,536 (4,294,967,296) would overflow. The FLI format stores dimension fields; the attacker sets them within the file without needing actual pixel data of that size.

Step 3 — Delivery and Execution The crafted FLI file is distributed via common channels — email attachment, a malicious download link, or embedded in a document. Social engineering ("animated icon" / "flipbook") induces the victim to open the file in GIMP. Upon opening, GIMP's file-fli plugin begins parsing and calculates the buffer size as width * height. The signed overflow yields a negative or otherwise insufficient buffer size. The plugin then reads or writes pixel data into an undersized allocation, causing memory corruption and ultimately a crash of the GIMP process.

Step 4 — Post-Exploitation Impact The observable impact is a denial of service: GIMP terminates unexpectedly. If the victim is mid-work on other GIMP projects, unsaved work may be lost. No privilege escalation or data exfiltration is indicated by the NVD description or CVSS vector (C:N/I:N). The attacker has no direct post-exploitation persistence — the impact is limited to the crash moment, though repeated delivery could cause recurring denial of service.

Impact Assessment

CVSS Score: 5.5 (Medium) — CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

• Attack Vector: Local (AV:L) — the file must be opened locally by the victim.
• Attack Complexity: Low (AC:L) — no special conditions beyond opening a file.
• Privileges Required: None (PR:N) — the attacker needs no privileges, only file delivery.
• User Interaction: Required (UI:R) — the victim must open the malicious file.
• Scope: Unchanged (S:U) — impact remains in GIMP.
• Confidentiality: None (C:N) — no data exposure indicated.
• Integrity: None (I:N) — no file modification or code execution indicated.
• Availability: High (A:H) — complete application crash (denial of service).

Affected Systems: Any GIMP build that includes the file-fli plugin, across all supported operating system platforms (Windows, Linux, macOS). Because the plugin is enabled by default in typical distributions, the affected population is broad.

Blast Radius: GIMP has a large user base among graphic designers, animators, and hobbyists. In an enterprise context, workstations running GIMP for image processing tasks are the primary at-risk population. While the impact is DoS-only and requires user interaction, the attack is trivial to produce once the exploit is developed (public PoC would lower skill barrier) and requires no authentication. Data-loss risk from unsaved work in a crashing process is the most direct enterprise concern.

Detection Guidance

Sigma Rule

title: Potential GIMP FLI File Exploitation - Process Crash on Malformed File
id: 8719c75e-3dbb-4b7a-b2b1-5c381d3f7b90
status: experimental
description: Detects GIMP process crashes or anomalous memory allocation failures that may indicate attempts to exploit CVE-2026-59088 (signed integer overflow in file-fli plugin).
author: Valters IT Threat Intelligence
date: 2026/05/03
tags:
    - attack.t1204
    - attack.t1499
    - cve.2026.59088
logsource:
    category: process_creation
    product: windows
detection:
    selection_gimp:
        Image|endswith:
            - '\gimp-2.10.exe'
            - '\gimp-2.99.exe'
            - '\gimp.exe'
    selection_fli:
        CommandLine|contains:
            - '.fli'
            - '.flc'
    condition: selection_gimp and selection_fli
falsepositives:
    - Normal opening of legitimate FLI files
    - GIMP command-line batch processing of FLI files
level: medium

YARA Rule

rule CVE_2026_59088_GIMP_FLI_Overflow
{
    meta:
        author = "Valters IT Threat Intelligence"
        description = "Detects FLI files crafted to exploit CVE-2026-59088 (signed integer overflow in GIMP file-fli plugin)"
        cve = "2026-59088"
        date = "2026-05-03"
        filetype = "FLI animation"
    strings:
        // FLI file magic number (0xA F L I) at offset 0
        $fli_magic = { 46 4C 49 0A }   // "FLI\x0A"
        $flc_magic = { 46 4C 43 1A }   // "FLC\x1A"
        // FLI/FLC header width field at offset 20 (little-endian)
        // Height field at offset 22
    condition:
        ($fli_magic or $flc_magic) and
        // Width * Height producing a signed 32-bit overflow condition
        uint16(20) != 0 and
        uint16(22) != 0 and
        uint32(20) > 0x7FFFFFFF
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-59088 GIMP FLI Malicious File Download Attempt"; flow:to_client,established; filemagic:"FLI"; fileext:"fli"; fileext:"flc"; content:"application/octet-stream"; nocase; classtype:attempted-dos; sid:202659088001; rev:1;)

alert http any any -> any any (msg:"CVE-2026-59088 GIMP FLI Signed Integer Overflow Potential Trigger"; flow:to_client,established; filemagic:"FLI"; fileext:"fli"; content:"|0A|"; distance:0; within:4; classtype:attempted-dos; sid:202659088002; rev:1;)

Elastic Detection

// Detect GIMP process crash events or crash dump creation following opening of FLI files
sequence by host.name with maxspan=10m
  [process where event.action == "start" and 
     process.name : ("gimp*", "gimp-2*.exe") and
     process.command_line : ("*.fli", "*.flc")]
  [process where event.action == "end" and 
     process.name : ("gimp*", "gimp-2*.exe") and 
     process.exit_code != 0]

Splunk SPL Query

index=windows sourcetype=WinEventLog:Security OR sourcetype=WinEventLog:System
| search (EventCode=1000 AND (Image="*gimp*")) OR (EventCode=1001 AND (Image="*gimp*")) OR (EventCode=7036 AND (Description="crash*"))
| eventstats values(Message) as crash_message by host
| search crash_message="*gimp*" OR crash_message="*GIMP*" OR crash_message="*file-fli*"
| table _time, host, user, EventCode, Image, Message
| sort - _time

Wazuh OSSEC Rule

<group name="gimp,">
  <!-- Detect GIMP crash events on Windows -->
  <rule id="100501" level="8">
    <if_sid>18100</if_sid>
    <match>gimp</match>
    <description>GIMP process crashed - potential CVE-2026-59088 exploitation</description>
    <group>dos,attack,</group>
  </rule>

  <!-- Detect GIMP crash on Linux -->
  <rule id="100502" level="8">
    <if_sid>100100</if_sid>
    <match>Segmentation fault</match>
    <match>gimp</match>
    <description>GIMP segmentation fault - potential CVE-2026-59088 memory corruption</description>
    <group>dos,memory_corruption,</group>
  </rule>

  <!-- Detect repeated GIMP crashes (correlation) -->
  <rule id="100503" level="10" frequency="3" timeframe="300">
    <if_matched_sid>100501</if_matched_sid>
    <description>Multiple GIMP crashes in short window - likely active exploitation attempt</description>
    <group>dos,attack,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No patch evidence from any tracked source, no vendor advisory, no CVE-specific fix has been identified. Affected versions are undefined; all GIMP installations with the file-fli plugin are presumed at risk until a patch is available.

1) Immediate Mitigations (until vendor patch available)

• Disable or remove the FLI plugin: If the organization does not require FLI/FLC format support, remove or rename the file-fli plugin binary for GIMP. On Linux this is typically located in /usr/lib/gimp/2.0/plug-ins/file-fli; on Windows in %ProgramFiles%\GIMP 2\lib\gimp\2.0\plug-ins\. Confirm the path for the installed GIMP version (the exact path was not further specified in the NVD data — if the plugin path cannot be located, remove GIMP entirely pending the vendor fix).
• Restrict opening of legacy animation formats: Implement a security policy prohibiting the opening of FLI/FLC files in GIMP. Add file-type filtering to email gateways to quarantine .fli and .flc attachments.
• Sandbox GIMP: Run GIMP in a virtualized or sandboxed environment (e.g., Windows Sandbox, Firejail on Linux) to contain crashes and prevent any potential data loss.

2) Patch / Upgrade Steps

• Monitor for the vendor advisory: Watch the official GIMP release notes (gimp.org) for a security-fix release. When a patched version is published (e.g., GIMP 2.10.x security update or a 3.0.x series fix), upgrade promptly.
• Check OS package repositories for backported fixes for GIMP packages used in Linux distributions.
• Track CVE-2026-59088 on NVD and vendor channels — when a patch lands, update the Patch Confidence score and re-assess.

3) Long-Term Hardening

• Enable GIMP's automatic file-type safety prompts and disable any "trusted file extensions" auto-open behaviors.
• Enforce the principle of least privilege on end-user workstations: run GIMP without administrative privileges.
• Implement endpoint security monitoring (as per Detection Guidance) to detect crashes and anomalous file-handling behavior — a single reproducible crash at GIMP upon opening a file is a strong indicator of malicious FLI activity.
• User awareness training: Educate users on opening unfamiliar files, especially legacy animation formats received from external parties.
• Maintain an asset inventory of GIMP installations to facilitate the rapid deployment of the pending vendor fix.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-59088
2. GIMP Official Website (vendor advisory pending): https://www.gimp.org/
3. GIMP Git Repository / Bug Tracker (watch for fix commit): https://gitlab.gnome.org/GNOME/gimp
4. CWE-190 — Integer Overflow or Wraparound (MITRE): https://cwe.mitre.org/data/definitions/190.html
5. ATT&CK — T1499 Endpoint Denial of Service: https://attack.mitre.org/techniques/T1499/

Threat Actor Activity / Exploit-in-the-Wild: No known campaigns utilizing CVE-2026-59088 have been observed as of report preparation. No exploit code has been publicly released. CISA KEV status is NO (not listed on the Known Exploited Vulnerabilities catalog) — no exploitation in the wild has been confirmed by any tracked source. Organizations should treat this as a latent risk pending public exploit development, at which point the threat level escalates.