CVE-2026-59091

Executive Summary

CVE-2026-59091 is an out-of-bounds write vulnerability (CWE-787) discovered in GIMP's file format plugins, specifically those handling PSD and PAA image files. A remote attacker can exploit this flaw by convincing a user to open a specially crafted image file, which may lead to unexpected application behavior, memory corruption, or arbitrary code execution with the privileges of the user running GIMP. Currently unpatched with no vendor fix available, the vulnerability carries a CVSS score of 7.3 (High) and requires local access and user interaction, making phishing campaigns the most likely infection vector.

Technical Analysis

The vulnerability resides within GIMP's file format parsing plugins, specifically the handlers for PSD (Photoshop Document) and PAA (Personal Ancestral File) image formats. The underlying weakness is classified as CWE-787, Out-of-bounds Write, indicating that the plugin writes data beyond the bounds of an allocated memory buffer during file parsing.

Vulnerability Mechanism: When GIMP processes a malformed PSD or PAA file, the parsing routine fails to properly validate size fields, offsets, or count values embedded within the file structure. This insufficient validation allows an attacker to control write offsets and lengths, causing the parser to write data outside the allocated heap buffer. The result is memory corruption that can be leveraged to overwrite adjacent heap metadata, function pointers, or other application state.

Attack Surface: The attack surface is the GIMP image processing engine itself, accessible whenever a user opens an image file. Since PSD is a widely used format in graphic design workflows, and PAA is used in genealogy software, the user base includes creative professionals and researchers who routinely handle files from untrusted sources.

Technical Detail Availability: The NVD description does not specify the exact code paths, function names, or buffer structures involved. Insufficient technical detail is available to pinpoint the precise parsing routines affected. However, based on the vulnerability class, the flaw likely involves:

1. Insufficient bounds checking on layer count or channel count fields in PSD headers
2. Unvalidated size fields used in memory allocation calculations
3. Integer overflow scenarios that lead to undersized allocations followed by oversized writes
4. Missing validation of chunk lengths in PAA file structure parsing

The CVSS vector emphasizes several important characteristics:

• AV:L (Local): The attacker must have access to the target system, typically by delivering a malicious file
• AC:L (Low Complexity): No special conditions are required beyond opening the file
• PR:L (Low Privileges): The attacker needs some form of local access, but this is typically satisfied by user-level access
• UI:R (User Interaction): The victim must open the crafted file — this is the primary requirement
• C/H/I:H (High Confidentiality/Integrity/Availability): Full impact achievable if exploited successfully

The EPSS score of 0.00167 (6.3rd percentile) indicates low current exploit activity in the wild, but this metric is dynamic and may increase as public awareness grows. The vulnerability is not listed on CISA's Known Exploited Vulnerabilities catalog.

Exploitation Scenarios

Based strictly on the NVD description and vulnerability class, the following attack chain is inferred:

Stage 1: Reconnaissance and Target Identification The attacker identifies potential victims among GIMP users — graphic designers, digital artists, photographers, or genealogy researchers. The attacker may use social engineering to establish trust, possibly through email, forums, or direct messaging platforms where image file sharing is common.

Step 2: Crafting the Malicious Payload The attacker crafts a malicious PSD or PAA file containing:

• Valid file signatures and headers that pass initial format validation (ensuring GIMP recognizes the file as a legitimate image)
• Deliberately corrupted or oversized size/count fields in specific structural sections (e.g., layer count, channel numbers, or color profile data) that trigger the out-of-bounds write
• Possibly embedding shellcode or ROP chain in the file data that will be written outside the intended buffer bounds

The file must be designed to trigger the flaw without corrupting the file structure to the point where GIMP rejects it outright.

Step 3: Delivery and Execution The attacker delivers the malicious file via:

• Email attachments (most likely vector given the phishing-related ATT&CK tactic)
• Download links on compromised websites or forums
• Shared collaboration platforms (e.g., cloud storage, design collaboration tools)

When the victim downloads and opens the file in GIMP, the parser begins processing the malformed structure. The out-of-bounds write occurs during parsing, corrupting heap memory. Depending on the exact corruption, this can lead to:

• Application crash (Denial of Service)
• Arbitrary code execution if the attacker can control the overwritten data to hijack control flow

Step 4: Post-Exploitation Impact Upon successful exploitation, the attacker achieves code execution in the context of the GIMP process. Potential post-exploitation activities include:

• Data Exfiltration: Reading files accessible to the user (especially valuable in design studios handling proprietary assets)
• Persistence: Installing backdoors or other malware that survives reboot
• Lateral Movement: Using the compromised system as a pivot point into the wider network

No public PoC is available; the attack chain is inferred from the vulnerability class and standard exploitation techniques for CWE-787.

Impact Assessment

Business Impact: The severity is high (CVSS 7.3) due to the confidentiality, integrity, and availability impacts all rated High. Organizations relying on GIMP for production workflows face:

• Intellectual Property Theft: Design files, proprietary graphics, and client assets could be exfiltrated
• System Compromise: Arbitrary code execution can lead to full system compromise
• Workflow Disruption: GIMP crashes render image processing pipelines unavailable
• Supply Chain Risk: If GIMP is used to process images from external collaborators or clients, a compromised file could introduce malware into trusted workflows

Affected Systems: All GIMP installations with PSD and PAA plugin support are potentially vulnerable. Given that no specific version range has been disclosed and no patch exists, all current versions of GIMP should be considered at risk until the vendor provides an update.

Blast Radius: The attack requires local file access and user interaction, limiting the blast radius to individual workstations. However, in enterprise environments where designers exchange files frequently, a single malicious file could compromise multiple systems as the file propagates through the organization.

CVSS Subscore Analysis:

• Attack Vector: Local (subscore 0.55)
• Attack Complexity: Low (subscore 0.77)
• Privileges Required: Low (subscore 0.62)
• User Interaction: Required (subscore 0.85)
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

Detection Guidance

Sigma Rule

title: Suspicious GIMP File Format Plugin Activity
id: 7a3c2d9e-5f4a-4b6c-8d1e-2f3a4b5c6d7e
status: experimental
description: Detects unusual GIMP process behavior potentially related to CVE-2026-59091 exploitation
author: Valtersit Threat Intelligence
date: 2026/01/15
logsource:
    category: process_creation
    product: windows
detection:
    selection_gimp:
        Image|endswith:
            - '\gimp-2.10.exe'
            - '\gimp-2.99.exe'
            - '\gimp.exe'
    selection_crash:
        EventID:
            - 1000  # Application Error
            - 1001  # Windows Error Reporting
    selection_anomaly:
        CommandLine|contains:
            - '*.psd'
            - '*.paa'
    condition: selection_gimp and (selection_crash or selection_anomaly)
levels:
    - medium
falsepositives:
    - Legitimate PSD files with unusual structures
    - GIMP crashes due to other bugs
tags:
    - attack.t1566
    - cve.2026.59091
    - cwe.787

YARA Rule

rule CVE_2026_59091_GIMP_PSD_PAA_MALICIOUS
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects potentially malicious PSD/PAA files targeting CVE-2026-59091"
        date = "2026-01-15"
        cve = "CVE-2026-59091"
        cwe = "CWE-787"
        severity = "high"
    strings:
        $psd_magic = { 38 42 50 53 }  // 8BPS (PSD signature)
        $paa_magic = { 50 41 41 46 }  // PAAF (PAA signature)
        $layer_marker = { 6C 61 79 65 72 }  // "layer"
        $chunk_marker = { 63 68 75 6E 6B }  // "chunk"
        $suspicious_size_1 = { FF FF FF 7F }  // Potential oversized size field
        $suspicious_size_2 = { FF FF FF FF }
    condition:
        uint32(0) == 0x38425053 or uint32(0) == 0x50414146
        and 2 of ($suspicious_size_*)
        and filesize > 100KB
}

Suricata IDS Rule

alert http any any -> any any (msg:"GIMP CVE-2026-59091 PSD File Download Attempt"; flow:established; content:"Content-Type|3a| image/psd"; nocase; content:"8BPS"; fast_pattern; distance:0; within:4; threshold:type both, track by_src, count 3, seconds 300; classtype:attempted-user; sid:202659091; rev:1; metadata:cve CVE-2026-59091;)

Elastic Detection

sequence with maxspan=5m
  [ file where event.action == "open" and (
      file.name : "*.psd" or file.name : "*.paa"
    ) and process.name : "gimp-*" ]
  [ process where event.action == "end" and exit_code != 0
    and process.name : "gimp-*" ]
  [ process where event.action == "start"
    and parent.process.name : "gimp-*"
    and (
      process.name : ("cmd.exe", "powershell.exe", "wscript.exe")
      or process.name : "*shell*"
    ) ]

Splunk SPL Query

index=windows sourcetype=WinEventLog:System
(EventCode=1000 OR EventCode=1001)
| search Image="*gimp*"
| rex field=Message "(?<faulting_module>[^\s]+\.dll)"
| stats count by host, Image, faulting_module
| where count > 2
| eval threat = "CVE-2026-59091 suspected GIMP crash loop"
| table _time, host, Image, faulting_module, count, threat

Wazuh OSSEC Rule

<group name="gimp,cve-2026-59091,">
  <rule id="807560" level="10">
    <decoded>
      <program_name>gimp</program_name>
    </decoded>
    <match>segmentation fault|memory corruption|heap corruption</match>
    <description>GIMP crash possibly related to CVE-2026-59091 PSD/PAA parser vulnerability</description>
    <group>gimp, cve-2026-59091,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Status: UNPATCHED — no patch evidence from any tracked source. The vendor has not released a fix, and no version range has been confirmed as affected or patched.

Immediate Mitigations:

1. User Education: Train users to not open PSD or PAA files from untrusted sources. Implement a policy requiring verification of file provenance before opening in GIMP.
2. Alternative Software: For critical workflows, consider using alternative image editing software or online PSD viewers until a patch is available.
3. Sandboxing: Run GIMP in a sandboxed environment (e.g., Firejail on Linux, Sandboxie on Windows, or a dedicated VM) to contain the impact of potential exploitation.
4. File Filtering: Implement email and web gateway filtering rules to block or quarantine PSD and PAA attachments from external sources.
5. Application Control: Use endpoint protection platforms with application whitelisting to restrict GIMP execution to validated scenarios.

Patch/Upgrade Steps:

1. Monitor GIMP's official website (https://www.gimp.org) and security advisories for patch releases.
2. The NVD database and vendor advisories should be checked regularly (NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59091).
3. Once a patched version is released, test it in a staging environment before enterprise deployment.
4. Subscribe to GIMP security mailing lists or RSS feeds for immediate notification of fixes.

Long-Term Hardening:

1. Least Privilege: Ensure GIMP runs with standard user privileges, never as administrator/root.
2. Memory Protection: Enable ASLR, DEP/NX, and other platform memory protections where applicable.
3. Regular Updates: Maintain GIMP installations at the latest stable version once patches become available.
4. Input Validation: For enterprises processing external images, consider a pre-screening process using alternative parsers or image validators before opening in GIMP.
5. Monitoring: Deploy the detection rules provided above to identify potential exploitation attempts.
6. Incident Response: Develop an incident response playbook specific to GIMP-related compromises, including containment procedures and forensic analysis guidelines.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-59091
2. GIMP Official Website: https://www.gimp.org
3. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE not currently listed)
4. MITRE ATT&CK — Phishing (T1566): https://attack.mitre.org/techniques/T1566/
5. CWE-787 Description: https://cwe.mitre.org/data/definitions/787.html

Threat Actor Campaigns: As of the writing of this report, no known threat actor campaigns exploiting CVE-2026-59091 in the wild have been documented. The CVE is not present in the CISA KEV catalog, and the EPSS score (0.00167) indicates low current exploitation probability. However, given the vulnerability's high CVSS score and the absence of a patch, the risk of future exploitation activity is elevated. Security teams should treat any unsolicited PSD/PAA files as potentially malicious until a patch is available.