CVE-2026-18308

Executive Summary

CVE-2026-18308 is a high-severity integer overflow vulnerability in GIMP's TIFF file parsing routines that enables remote code execution in the context of the current user. The flaw, tracked as ZDI-CAN-29405 by the Zero Day Initiative, requires victim interaction — opening a malicious TIFF file or visiting a malicious page — to trigger exploitation. Affected organizations are those deploying GIMP as a desktop image-editing application, particularly in production graphics pipelines, media production environments, or any enterprise workstation where GIMP is installed. Successful exploitation yields full code execution with the privileges of the logged-in user, enabling data theft, lateral movement, or ransomware deployment depending on the target environment.

Technical Analysis

CVE-2026-18308 is classified under CWE-190 (Integer Overflow or Wraparound). The vulnerability resides in GIMP's parsing of TIFF (Tagged Image File Format) files. The NVD description states the root cause is "the lack of proper validation of user-supplied data, which can result in an integer overflow before allocating a buffer."

The vulnerability mechanism is a classic integer overflow leading to a buffer overflow (often termed an "integer overflow-to-buffer overflow" chain). When GIMP parses a crafted TIFF file, it processes various numeric fields such as image dimensions, strip offsets, byte counts, or tile parameters. Attackers craft specific 32-bit (or other width) numeric values in the TIFF structure that, when manipulated in arithmetic operations during parsing, cause the computed result to wrap around past the maximum representable integer value. The resulting overflowed value is then used as the size parameter for a memory allocation call. Because the overflowed value is typically very small (or unexpectedly large but insufficiently validated), the subsequent buffer write operations assume a different buffer capacity than what was actually allocated. This mismatch creates a classic heap-based buffer overflow condition: the parser writes data beyond the bounds of the undersized allocation, corrupting adjacent heap metadata or application data structures. An attacker who controls the TIFF content can leverage this corruption to achieve arbitrary code execution.

No specific function names, class names, or API endpoints are disclosed in the NVD description. The attack surface is the TIFF file import code path within GIMP, which is reachable through multiple entry points: direct file open, drag-and-drop, image import via scripting interfaces, or automatic preview/thumbnailing operations. Because GIMP is often integrated into automated workflows via command-line batch processing (e.g., gimp -i -b scripts) or via the GEGL (Generic Graphics Library) backend, affected deployments include both interactive desktop use and semi-automated processing pipelines.

Exploitation Scenarios

Based on the NVD description and vulnerability classification, the attack chain is inferred as follows. No public PoC exists; therefore, the chain reflects the expected exploitation methodology for this vulnerability class.

Step 1: Reconnaissance / Target Identification. An attacker identifies environments where GIMP is installed — for example, graphic design agencies, publishing houses, media companies, or workstations in engineering departments. The attacker may use social engineering, phishing lures, or compromised websites to craft a delivery mechanism. Alternatively, malicious files could be distributed via email attachments, shared project repositories, FTP sites, or compromised asset-download portals.

Step 2: Triggering the Flaw. The attacker crafts a malformed TIFF file containing integer values calculated to trigger an overflow condition during GIMP's parsing. The target user must open this file (double-clicking the file, opening via GIMP's File→Open dialog, or dragging it onto an open GIMP window). The NVD description also mentions "visit a malicious page," suggesting that browser-based TIFF handling linked to GIMP (e.g., via handler registration) or web-based GIMP integrations could also be exploitation vectors. The crafted values cause the integer overflow during buffer-size computation.

Step 3: Payload Execution. When the overflow occurs, the undersized heap buffer is subsequently overflowed with attacker-controlled TIFF data. The attacker manipulates this to corrupt heap metadata or application pointers, achieving arbitrary write primitives. On modern platforms, this typically requires a secondary stage: heap grooming to shape allocations, followed by overwriting a function pointer, vtable entry, or exception handler. The attacker then triggers a code execution path where control flow is redirected to attacker-controlled memory (e.g., a heap spray or a ROP chain). The payload executes with the privileges of the current GIMP process.

Step 4: Post-Exploitation Impact. Once code execution is achieved in the GIMP process context, the attacker inherits the user's privileges. On a single-user workstation, this may mean full access to user files, credentials stored in the keychain/browser, and the ability to install persistence mechanisms, keyloggers, or ransomware. In enterprise environments where GIMP runs on shared machines or where the user has elevated privileges, the impact expands to network lateral movement, sensitive document exfiltration, or data encryption. No public PoC is available; the attack chain is inferred from the vulnerability class.

Impact Assessment

The CVSS vector CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H scores 7.8 (High). Key attributes: The attack vector is Local (AV:L) — the attacker must have the file or provide it locally (as opposed to network-based exploitation against a listening service), but the delivery can be remote via phishing or web-based means. Attack complexity is Low (AC:L). No privileges are required (PR:N). User interaction is Required (UI:R) — the victim must open the malicious file or visit a malicious page. The scope is unchanged (S:U). The confidentiality, integrity, and availability impacts are all rated High.

Business impact includes: compromise of the user's workstation and all accessible data; potential pivot point into the corporate network; and disruption of graphics production workflows if ransomware or destructive payloads are deployed. The EPSS score of 0.00339 (26.6 percentile among exploited CVEs) indicates a relatively low but growing probability of exploitation. The vulnerability is not listed in CISA's Known Exploited Vulnerabilities catalog, and no exploit-in-the-wild evidence has been published to date.

Detection Guidance

Sigma Rule

title: GIMP TIFF Parsing Integer Overflow Exploitation Attempt
id: 663a94dc-71c1-4c58-8a3e-91c28bb31901
status: experimental
description: Detects GIMP process crashes or abnormal memory permissions that may indicate TIFF file parsing exploit attempts
logsource:
    category: process_creation
    product: windows
detection:
    selection_gimp:
        Image|endswith:
            - '\gimp-2.10.exe'
            - '\gimp-2.99.exe'
            - '\gimp-win32.exe'
        CommandLine|contains:
            - '.tif'
            - '.tiff'
    selection_crash:
        EventID: [1000, 1001]  # Application Error / Windows Error Reporting
    condition: selection_gimp and selection_crash
level: high
falsepositives:
    - Legitimate crashes of GIMP on malformed (not malicious) TIFF files
fields:
    - CommandLine
    - Image
tags:
    - attack.execution
    - attack.t1203
    - cve.2026-18308

YARA Rule

rule GIMP_TIF_IntegerOverflow_ZDI_CAN_29405 {
    meta:
        author = "ValtersIT Threat Intelligence"
        description = "Detects TIFF files with anomalous integer fields indicative of CVE-2026-18308 integer overflow exploitation attempts"
        date = "2026-01-01"
        cve = "CVE-2026-18308"
        zdi = "ZDI-CAN-29405"
        reference = "NVD CVE-2026-18308"
    strings:
        // TIFF magic bytes - little-endian and big-endian variants
        $tiff_le = { 49 49 2A 00 }
        $tiff_be = { 4D 4D 00 2A }
        // Common TIFF integer fields often targeted:
        // ImageWidth (Tag=256), ImageLength (Tag=257), StripByteCounts (Tag=279), StripOffsets (Tag=273)
        $tag_imagewidth = { 00 01 00 00 }   // Tag 256 little-endian
        $tag_imagelength = { 01 01 00 00 }  // Tag 257 little-endian
        $tag_stripoffsets = { 11 01 00 00 } // Tag 273 little-endian
        $tag_stripbytecounts = { 17 01 00 00 } // Tag 279 little-endian
        // Anomalous large value patterns: 0xFF000000 to 0xFFFFFFFF range (potential overflow candidates)
        $huge32_1 = { FF FF FF 7F }
        $huge32_2 = { FF FF FF FF }
    condition:
        filesize > 100KB and
        uint16(0) == 0x4949 and // little-endian TIFF
        (uint16(2) == 42) and
        any of ($tag_*) and
        (any of ($huge32_*))
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (
    msg:"GIMP TIF Parsing Integer Overflow Attempt (CVE-2026-18308)";
    flow:to_client,established;
    file.magic;
    content:"II";
    file.data;
    content:"|2A 00|";
    depth:4;
    within:4;
    threshold:type limit, track by_src, seconds 60, count 1;
    reference:cve,2026-18308;
    reference:url,https://nvd.nist.gov/vuln/detail/CVE-2026-18308;
    classtype:attempted-user;
    sid:202618308;
    rev:1;
    priority:1;
)

Elastic Detection

sequence by process.entity_id with maxspan=30s
  [process where event.type == "start" and
   process.name : "gimp*" and process.args : ("*.tif", "*.tiff")]
  [process where event.type == "end" and
   process.name : "gimp*" and process.exit_code != 0]
| stat count() as crash_count by process.name, process.entity_id

Splunk SPL Query

index=windows OR index=sysmon earliest=-7d
  (EventCode=4688 OR EventCode=1)
  (Image=*gimp* OR NewProcessName=*gimp*)
  (CommandLine=*.tif OR CommandLine=*.tiff OR CommandLine=*.TIF OR CommandLine=*.TIFF)
| stats count by host, user, CommandLine, Image
| where count > 1
| table _time, host, user, CommandLine, Image, count
| sort - _time

Wazuh OSSEC Rule

<rule id="183081" level="12">
    <if_sid>18100</if_sid> <!-- Generic process execution group -->
    <match>gimp</match>
    <description>CVE-2026-18308 - GIMP process executed with TIFF file argument (potential targeted exploit)</description>
    <group>gimp,tiff,cve,exploit,attack</group>
    <mitre>
        <id>T1203</id>
    </mitre>
</rule>
<rule id="183082" level="15">
    <if_sid>183081</if_sid>
    <match>\.(tif|tiff)</match>
    <description>CVE-2026-18308 - GIMP launched with TIFF file - potential triggering of integer overflow</description>
    <group>gimp,tiff,cve,exploit,attack</group>
    <mitre>
        <id>T1203</id>
    </mitre>
</rule>

Mitigation & Patch Guidance

Patch confidence is rated 4/4 — confirmed by 3 or more independent sources (NVD, Debian, RHSA have all acknowledged a fix). Despite the Affected Versions field being empty in the available metadata, the patch status is confirmed.

1) Immediate mitigations (if unable to patch immediately):

• Disable or restrict GIMP's auto-preview and thumbnail generation for untrusted directories.
• Use sandboxing solutions (e.g., AppArmor, SELinux, Windows Sandbox) when handling untrusted TIFF files.
• Set file association policies to require explicit user confirmation before opening image files.
• Block email attachments with .tif/.tiff extensions at the gateway, particularly when the sender is untrusted.
• Monitor GIMP process crashes on workstations as a possible indicator of exploit attempts.

2) Patch / Upgrade Steps:

• Update GIMP to the latest available version from the official vendor. Red Hat (RHSA), Debian, and NVD all confirm a fixed version exists.
• For Debian-based systems: apt update && apt upgrade gimp (after confirming the fixed package is available).
• For Red Hat-based systems: yum update gimp or dnf update gimp.
• For manual installations: download the latest release from the official GIMP website and replace the vulnerable binaries.

3) Long-term hardening:

• Enforce a policy of opening image files only from trusted sources, even when patched — defense in depth against future 0-days.
• Implement an endpoint detection and response (EDR) platform that monitors for unusual process behavior and memory corruption indicators.
• For high-security environments, evaluate alternatives to GIMP or restrict its use to isolated virtual machines or containers.
• Keep all graphical processing software up to date; image parsers are a persistent attack surface across many applications (e.g., browsers, document viewers, media players).
• Review NVD and CISA KEV feeds regularly for updates on this CVE — the EPSS percentile of 26.6% indicates exploitation likelihood is expected to rise over time.

References

1. NVD Entry — CVE-2026-18308: https://nvd.nist.gov/vuln/detail/CVE-2026-18308
2. ZDI Reference — ZDI-CAN-29405 (referenced in NVD description): https://www.zerodayinitiative.com/advisories/ (search for ZDI-CAN-29405)
3. Debian Security Tracker — CVE-2026-18308: https://security-tracker.debian.org/tracker/CVE-2026-18308
4. Red Hat Security Advisory (RHSA) — CVE-2026-18308: https://access.redhat.com/security/cve/CVE-2026-18308
5. CISA KEV Catalog — This CVE is NOT listed (last referenced 2026); monitor: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat Actor Activity: No known threat actors have publicly claimed or been attributed to exploitation of CVE-2026-18308. No exploit-in-the-wild evidence has been confirmed. However, the ZDI disclosure (ZDI-CAN-29405) indicates this may have been reported by a third-party researcher and could see incorporation into exploit kits or ransomware toolkits in the future, given the ease of TIFF file delivery via phishing. Continued monitoring of public exploit repositories and the CISA KEV catalog is advised.