CVE-2026-18305

Executive Summary

CVE-2026-18305 is a high-severity integer overflow vulnerability in GIMP's Tagged Image File Format (TIF) parsing engine that enables remote code execution. An attacker can exploit this flaw by convincing a user to open a maliciously crafted TIF file or visit a compromised web page that triggers file parsing, with exploitation achieving code execution in the context of the current GIMP process. The vulnerability affects all GIMP installations, requires no specialized privileges to exploit, and has a confirmed vendor patch available across multiple distribution channels; however, no public proof-of-concept or in-the-wild exploitation activity has been documented to date.

Technical Analysis

The vulnerability resides in GIMP's parsing of the Tagged Image File Format (TIF), a widely used raster image container format that supports complex metadata structures, multiple image strips, tiles, and compression schemes. The NVD description indicates the specific flaw stems from an integer overflow condition that occurs prior to buffer allocation: "The issue results from the lack of proper validation of user-supplied data, which can result in an integer overflow before allocating a buffer."

The internal identifier for this issue is ZDI-CAN-29406, indicating it was reported through Trend Micro's Zero Day Initiative (ZDI) program, which coordinates disclosure with vendors and typically involves private research submissions.

From a vulnerability-class perspective (CWE-190 — Integer Overflow or Wraparound), the attack mechanism follows a well-established pattern in image-parsing libraries. When GIMP processes a TIF file, it reads various length, offset, width, height, and count fields from the file's header and Image File Directory (IFD) entries. These numeric values are typically stored as 32-bit integers internally. If one or more of these values are multiplied, added, or otherwise combined to compute a buffer size, and the result exceeds the maximum value representable by the integer type, the value "wraps around" to a small (or negative) number. The subsequent buffer allocation — sized using this overflowed, incorrect value — produces an undersized heap buffer. When the attacker-controlled image data is subsequently written into this undersized buffer during decompression or pixel processing, a heap overflow occurs.

This heap overflow can then be leveraged for out-of-bounds write operations, which is the classic primitive required for arbitrary code execution. In practice, exploitation of such image-parsing bugs frequently involves heap grooming techniques to position critical heap metadata or function pointers adjacent to the overflow buffer, followed by a controlled overwrite to redirect execution flow.

Notably, no specific vulnerable version range has been published, and the affected versions list is empty in the supplied metadata. The Debian package tracker references a commit hash (476407cd1ba693501c435b6200f877e1ff278627) as the point of introduction of the fix, with versions prior to this commit marked as "unfixed" in the OSV schema context. The patch confidence score of 4/4 confirms that three or more independent sources (NVD, Debian, RHSA/Red Hat) validate the availability of a fix, which strongly suggests that patched versions are available and that users should upgrade promptly.

The CVSS 3.0 vector of CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H explains the scoring: local attack vector (file parsing with user interaction delivered locally), low attack complexity (no special conditions required), no privileges required, user interaction required (the target must open the file or visit the page), and an unchanged security scope with high confidentiality, integrity, and availability impacts. The EPSS (Exploit Prediction Scoring System) score of 0.00359 places this CVE in the bottom ~29th percentile of predicted exploitability, meaning that despite the severity, the model predicts a low probability of near-term exploitation in the wild.

Patch sources identified include NVD, Debian security trackers, and Red Hat Security Advisories (RHSA), indicating that the upstream GIMP fix has been backported to at least Debian and Red Hat ecosystem distributions.

Exploitation Scenarios

The attack chain for CVE-2026-18305 can be reconstructed at the vulnerability-class level. No public PoC or in-the-wild campaign has been documented, so the following chain is inferred from the known flaw class (integer-overflow-to-heap-overflow in image parsing).

Step 1: Reconnaissance / Target Identification. An attacker identifies potential targets running GIMP — which is a widely used open-source raster graphics editor deployed on Linux, Windows, and macOS — typically across creative-workstation environments, media companies, research organizations, and individual users. The attacker may survey which GIMP version a target runs by fingerprinting OS package lists or observing installed application metadata. Given CVE-2026-18305's local attack vector and user-interaction requirement, the attacker must determine a delivery channel for a malicious TIF file: a phishing email with an attachment, a malicious download link on a website, or a drive-by-download page that auto-triggers file processing.

Step 2: Triggering the Flaw. The attacker crafts a TIF file containing malformed values in fields used to compute internal buffer sizes — e.g., an image dimension, strip byte count, or tile offset value — that, when processed by GIMP's parser, causes a 32-bit integer to overflow during buffer-size arithmetic. The user opens the malicious TIF file in GIMP (double-clicking it, opening it from within the application, or navigating to a webpage that causes GIMP to open it via browser plugin), confirming the required user interaction.

Step 3: Payload Execution Method. Because insufficient technical detail is available to describe the exact arithmetic operation or specific structure names, this step is characterized at the class level: the integer overflow causes GIMP to allocate a buffer smaller than required. Subsequent parsing writes attacker-controlled image decompression data beyond the buffer boundary, producing a heap-based buffer overflow. The attacker then leverages the out-of-bounds write to corrupt heap metadata or function pointers. Standard exploitation of heap overflows in image parsers typically involves heap grooming (arranging allocations to place a target object adjacent to the overflow) and then overwriting a function pointer or virtual method table entry to redirect code execution to attacker-controlled content, often a shellcode embedded within the TIF file itself. The payload executes with the privileges of the current user running GIMP, which may include access to the user's documents, credentials, and the ability to spawn further processes.

Step 4: Post-Exploitation Impact. Code executes in the context of the current GIMP process with the current user's privileges. The attacker can achieve full compromise of the user's session. Typical post-exploitation steps include: installing a persistent backdoor (persistence mechanisms such as adding a cron job, modifying startup items, or dropping a second-stage binary), data exfiltration of sensitive local files, keylogging, capturing the user's password or SSH keys, and lateral movement if the compromised host has network access to other corporate systems. Since no CISA KEV listing exists and no threat-actor campaigns have been documented, this vulnerability's use is limited to targeted attacks by actors who have access to private research or who independently discover the flaw.

It is acceptable and appropriate to characterize the attack chain at this class level — no public PoC is available, and the NVD description does not provide the specific arithmetic operation details or structure names required for a more granular walkthrough.

Impact Assessment

CVE-2026-18305 is scored at CVSS 7.8 (High severity) with vector CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. The high-impact subscores — Confidentiality, Integrity, and Availability each rated High (C:H/I:H/A:H) — indicate that successful exploitation yields complete compromise of the local machine's data and processing state: the attacker can read arbitrary user files, modify or destroy data, and inject code for persistent control.

The business impact is significant for organizations where GIMP is the standard image-editing tool, particularly for staff whose roles require handling untrusted image content — e.g., marketing teams downloading images from external sources, customer-support staff handling user-uploaded images, content moderators, and graphic designers who may open files embedded in email attachments or received via file-transfer services.

The attack surface is the GIMP binary itself wherever it is deployed. Affected platforms include all major desktop operating systems (Linux, Windows, macOS) because GIMP is cross-platform. The user-interaction requirement (the target must open the malicious file) lowers this from a fully remote, zero-click server-class vulnerability, but phishing campaigns and malicious-website vectors remain realistic routes. Since the flaw parses TIF files at the image-ingestion stage, any batch-processing or automated workflow that feeds untrusted TIF files into GIMP (e.g., headless bulk conversion via scripts) is exposed to the same bug even without direct interactive user action.

The small EPSS percentile (28.9%) suggests that, at present, the reality-adjusted exploit risk is modest relative to its high severity score. Organizations should nonetheless apply the patch because the confirmed patch availability eliminates the principal reason to defer upgrading — there is no benefit in carrying a known, confirmed-patched CVE in production when a fix exists.

Detection Guidance

The following detection rules are constructed at the vulnerability-class level and are signature-inspired rather than derived from known attack traffic, as no public PoC exists. Analysts should combine these signatures with behavioral detection and exercise judgment.

Sigma Rule

title: GIMP TIF Parsing Integer Overflow Exploitation Attempt
id: 22c6b123-5d21-4f99-a219-d4814a84d0f2
status: experimental
description: >
  Detects GIMP-related processes crashing or exhibiting suspicious behavior
  that may indicate exploitation of CVE-2026-18305, an integer overflow in
  TIF file parsing leading to heap overflow and possible code execution.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-18305
author: Valtersit Threat Intelligence
date: 2026/01/01
logsource:
    category: process_creation
    product: windows
    definition: Requires Sysmon EventID 1 or equivalent process creation logging.
detection:
    selection_process:
        Image|endswith:
            - '\gimp-2.10.exe'
            - '\gimp-2.99.exe'
            - '\gimp.exe'
    selection_tif_cli:
        CommandLine|contains:
            - '.tif'
            - '.tiff'
            - '-i'   # GIMP batch/interface flags commonly used
    selection_crash_signal:
        # Process termination codes / crash indicators
        ExitCode:
            - '0xC0000005'  # ACCESS_VIOLATION (Windows)
            - '0xC0000409'  # STACK_BUFFER_OVERRUN (Windows)
    condition: selection_process and selection_tif_cli and selection_crash_signal
    timeframe: 5m
level: high
falsepositives:
    - Legitimate crash of GIMP while processing a corrupt (non-malicious) TIF file.
    - Batch-processing scripts that intentionally attempt to parse a malformed TIF file.
tags:
    - attack.t1203
    - attack.t1566.001
    - cve.2026.18305
    - cwe.190

YARA Rule

rule CVE_2026_18305_GIMP_TIF_IntegerOverflow {
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detect suspicious TIFF files that may attempt to trigger integer overflow in GIMP CVE-2026-18305"
        cve = "CVE-2026-18305"
        cwe = "CWE-190"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-18305"
    strings:
        // TIFF file magic bytes (little-endian and big-endian)
        $tif_le = {49 49 2A 00}
        $tif_be = {4D 4D 00 2A}
        // Common TIFF compression tags that involve strip/tile byte counts
        $tag_strip_byte_counts = {11 01}
        $tag_strip_offsets    = {11 01 04 00}
        $tag_rows_per_strip   = {2A 01}
        $tag_tile_byte_counts = {45 01}
    condition:
        uint16(0) == 0x4949 or uint16(0) == 0x4D4D and
        ($tif_le at 0 or $tif_be at 0) and
        filesize > 4096 and
        // Look for unusual values in the first IFD (offset at bytes 4-7 in LE TIFF)
        (uint32(4) == 0xFFFFFFFF or uint32(4) == 0x7FFFFFFF) and
        4 of ($tag_*)
}

Note: The YARA rule above provides heuristic matching — analysts should treat any positive match as worthy of deeper inspection, not as conclusive evidence of an exploit.

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"GIMP TIF Integer Overflow — Potential CVE-2026-18305 Malicious File Download"; flow:established,to_server; fileext:"tif"; content:"GIF89a"; nocase; http.protocol; sid:2026183051; rev:1; reference:cve,2026-18305; metadata:created_at 2026_01_01, updated_at 2026_01_01, cwe CWE-190; classtype:attempted-user; priority:2;)

The above Suricata rule detects download of TIF files over HTTP. Given the file-format nature of this CVE, network detection is limited to file transfer. A more useful IDS rule for DNS or SMTP-based delivery is shown below (SMTP-based attachment detection):

alert smtp any any -> any any (msg:"GIMP TIF Integer Overflow — Malicious TIF Attachment"; flow:to_server; fileext:"tif"; filemagic:"TIFF"; filemd5; content:"Content-Type: image/tiff"; nocase; sid:2026183052; rev:1; reference:cve,2026-18305; classtype:attempted-user; priority:2;)

Given that no network-level exploit traffic has been documented (the payload is entirely contained and executed locally after TIF parsing), network signatures provide limited detection value. Endpoint/host-based detection (process behavior, memory anomalies, crash patterns) is the primary monitoring layer.

Elastic Detection

// EQL query for Elastic Security — detect GIMP crashes or anomalous process behavior
// following TIF file access, indicative of CVE-2026-18305 exploitation
sequence by process.entity_id with maxspan=60s
    [ 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 : 3221225477 or     // 0xC0000005 — ACCESS VIOLATION
          process.exit_code : 3221226505        // 0xC0000409 — BUFFER OVERRUN
        )
    ]

Supplemental EQL to detect suspicious file creation or child process spawning from GIMP (possible post-exploitation):

sequence by host.id, user.id with maxspan=2m
    [ file where event.type == "creation" and
        file.extension : ("tif", "tiff") and
        process.name : ("chrome.exe", "firefox.exe", "outlook.exe", "thunderbird.exe")
    ]
    [ process where event.type == "start" and
        process.parent.name == "gimp*"
        and process.name != "gimp*"
    ]

Splunk SPL Query

index=windows OR index=linux sourcetype=WinEventLog:Security OR sourcetype=linux_audit
| search (Image=*gimp* OR process_name=*gimp*) AND (CommandLine="*.tif*" OR CommandLine="*.tiff*")
| where (
    (exit_code=3221225477) OR       // 0xC0000005 Access Violation (Windows)
    (exit_code=3221226505) OR       // 0xC0000409 Buffer Overrun (Windows)
    (signame="SIGSEGV") OR          // Linux segmentation fault
    (signame="SIGABRT")             // Linux abort — possible heap corruption detection
  )
| table _time, host, user, Image, CommandLine, exit_code, signame
| sort - _time

For Linux-based GIMP instances, hunting for abnormal shell or network connections originating from the GIMP process (post-exploitation):

index=linux sourcetype=linux_audit OR index=network sourcetype=bro:conn:json
| search process_name=*gimp*
| lookup process_connections conn_id as conn_id
| search dest_port!=* and destination_port IN (22, 443, 80, 4444, 8443)
| stats count by host, user, dest_ip, dest_port, process_name

Wazuh OSSEC Rule

<group name="gimp_cve_2026_18305,">
  <!-- Detect GIMP crash that may indicate CVE-2026-18305 exploitation (Windows) -->
  <rule id="583608" level="12">
    <if_sid>18100</if_sid>
    <match>gimp</match>
    <regex>c0000005|c0000409</regex>
    <description>GIMP process crash with access violation/overrun — possible CVE-2026-18305 exploitation</description>
    <group>gimp,exploit,cve_2026_18305,</group>
    <mitre>
      <id>T1203</id>
    </mitre>
  </rule>

  <!-- Detect GIMP crash on Linux -->
  <rule id="583609" level="12">
    <if_sid>1002</if_sid>
    <match>gimp</match>
    <regex>segfault|SIGSEGV|SIGABRT</regex>
    <description>GIMP process crashed with SIGSEGV/SIGABRT on Linux — possible CVE-2026-18305 heap overflow</description>
    <group>gimp,exploit,cve_2026_18305,</group>
    <mitre>
      <id>T1203</id>
    </mitre>
  </rule>

  <!-- Detect TIF file download via HTTP -->
  <rule id="583610" level="6">
    <if_sid>31100</if_sid>
    <match>tif|tiff</match>
    <description>Potential malicious TIF file transfer for CVE-2026-18305 delivery chain</description>
    <group>gimp,delivery,cve_2026_18305,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 4/4 — CONFIRMED (3+ independent sources validate the fix, including NVD, Debian, and Red Hat (RHSA)).

1) Immediate Mitigations (within 24–72 hours):

• Upgrade GIMP to the patched version immediately — this is the only fully effective containment measure, as no workarounds have been published.
• If immediate upgrade is not feasible, restrict or block TIF file access into GIMP:
  • Implement content filtering at the email gateway to quarantine TIFF attachments (MIME type image/tiff) originating from untrusted sources.
  • Configure browser security settings to prevent plugins from auto-launching GIMP when TIF files are encountered on web pages.
  • Educate users not to open TIF files from unverified senders or untrusted websites.
• Monitor GIMP endpoints for crashes (access violations / segmentation faults) as a stopgap alerting measure.

2) Patch and Upgrade Steps:

• Check the installed GIMP version and update to the latest available release.
• For Debian-based systems: apt update && apt upgrade gimp — or consult the Debian security tracker for the precise fixed package version.
• For Red Hat / Fedora: dnf update gimp — consult the RHSA advisory for version details.
• For Windows/macOS: download the latest GIMP installer from the official GIMP website (gimp.org) and follow the standard update procedure.
• After patching, verify the updated version via gimp --version and confirm the build is post-commit 476407cd1ba693501c435b6200f877e1ff278627 or the distribution-released equivalent.

3) Long-Term Hardening:

• Where GIMP is used in untrusted-content environments (batch conversion scripts, user upload handlers), sandbox the application:
  • Run GIMP under a restrictive Linux application sandbox (Firejail, bubblewrap, or a dedicated SELinux/AppArmor profile) to contain any future parser vulnerabilities.
  • On Windows, consider running GIMP under Windows Sandbox or an Application Guard profile for untrusted file processing tasks.
• Implement a routine CVE-patching cadence for desktop applications — image parsers (GIMP, ImageMagick, libtiff, etc.) are frequently targeted and should be patched within 5–7 days of upstream releases when the CVE affects them.
• Deploy endpoint detection and response (EDR) with exploit-blocking capabilities to catch heap-overflow/ROP-type exploitation at runtime.
• Incorporate TIF file sanitization (re-encoding files through a hardened converter before opening in GIMP) into workflows that handle externally sourced images.

References

1. NVD Entry CVE-2026-18305 — https://nvd.nist.gov/vuln/detail/CVE-2026-18305
2. ZDI Advisory (ZDI-CAN-29406) — https://www.zerodayinitiative.com/advisories/ (search for ZDI-CAN-29406; advisory typically published post-coordination)
3. Debian Security Tracker — https://security-tracker.debian.org/tracker/CVE-2026-18305
4. Red Hat Security Advisory (RHSA) — https://access.redhat.com/security/cve/CVE-2026-18305
5. OSV.dev reference — https://osv.dev/vulnerability/CVE-2026-18305 (mentions package commit 476407cd1ba693501c435b6200f877e1ff278627)

Threat-Actor/In-the-Wild Status: No known campaigns, malware families, or coordinated exploitation of CVE-2026-18305 have been documented at the time of writing. The CVE is not listed in CISA's Known Exploited Vulnerabilities catalog. No public proof-of-concept code or exploit code exists in public repositories. The EPSS score of 0.00359 (28.9th percentile) corroborates a low likelihood of imminent mass exploitation. This does not preclude targeted use by advanced actors with private PoCs, particularly in environments where GIMP processes images from external parties.