CVE-2026-82324

Executive Summary

CVE-2026-82324 is an unpatched heap out-of-bounds read vulnerability in the file-iff (IFF/ILBM) plugin of GIMP, a widely deployed open-source raster graphics editor. The flaw is triggered when a user opens a specially crafted IFF/ILBM image file, and is caused by improper validation of HAM row size combined with mishandling of a zero nPlanes value. Successful exploitation results in an application crash (denial of service) or, in limited cases, the disclosure of heap memory contents. The attack vector is local and requires user interaction (the victim must open the malicious file); no remote exploitation path or public exploit code has been identified, and no patch is currently available from any vendor source.

Technical Analysis

The vulnerability resides in the IFF/ILBM (Interchange File Format / Interleaved Bitmap) image parsing plugin within GIMP. The technical details available from the NVD description are limited but sufficient to characterize the flaw class and its mechanism.

Vulnerability Class: CWE-125 — Out-of-bounds Read (heap context).

Root Cause Mechanism: The file-iff plugin fails to validate the HAM row size parameter when parsing an IFF/ILBM file. HAM (Hold-And-Modify) is a legacy Amiga graphics mode that allows a limited palette to create many colors by modifying the RGB components of the previous pixel. Additionally, the plugin improperly handles a file where the number of color planes (nPlanes) is declared as zero. The combination of an unvalidated HAM row size and a zero plane count creates a row size mismatch — the calculated buffer row size does not match the actual data layout expected by the parser.

Memory Corruption Flow: When the parser iterates over the image rows and planes to decode HAM-encoded pixel data, it computes the expected row stride or buffer offset using the declared (and unvalidated) HAM row size and plane count. A zero nPlanes value produces an undersized allocation or a miscomputed arithmetic base, while the HAM row size determines the loop boundaries. The mismatch between the allocated buffer (derived from one set of parameters) and the read loop bounds (derived from the other) results in the decoder reading data beyond the heap allocation boundary. This is a classic bounds-checking bypass: the parser trusts two independent fields without cross-validating them against each other or against the allocation size.

Attack Surface: The attack surface is the file-opening pathway in GIMP. Because the vulnerable component is the file-iff plugin, the trigger is explicit: a user opens an .iff or .ilbm file (or a file with an IFF container). This can be delivered via phishing emails, malicious downloads, web content that auto-opens the file, or any other means by which a user is convinced to open a crafted image in GIMP. The plugin runs with the privileges of the user executing GIMP.

Code-Level Context: Specific function or class names are not disclosed in the NVD description, and insufficient technical detail is available to identify precise code paths beyond the plugin-level description. The vulnerability exists because the plugin does not cross-validate nPlanes (zero value) against the HAM row size before performing memory operations. The technical mechanism at the class level is: untrusted file-controlled integers influence both an allocation size and a loop bound, and the lack of enforcement of the invariant loop_bound <= allocation_size produces the OOB read.

Exploitation Scenarios

No public PoC or exploit code has been identified, and no in-the-wild exploitation has been confirmed. The following attack chain is inferred from the vulnerability class and the NVD description.

Step 1 — Reconnaissance / Target Identification: An attacker identifies a target organization or individual that uses GIMP. The attacker crafts a malicious IFF/ILBM image file. This requires knowledge of the IFF/ILBM file format and the specific parameter layout, specifically the fields controlling HAM mode row size and the nPlanes (plane count) field. The attacker sets nPlanes to zero and inserts a HAM row size larger than the actual row size, or otherwise configures the two fields to be inconsistent.

Step 2 — Triggering the Flaw: The attacker delivers the malicious .iff/.ilbm file to the victim. Delivery methods include email attachment, a compromised website, a torrent, or removable media. The victim opens the file using GIMP (File → Open, or drag-and-drop). The file-iff plugin begins parsing the IFF container and the ILBM bitmap chunk.

Step 3 — Payload / Execution at the Vulnerability-Class Level: During the parsing of the bitmap data, the plugin uses the inconsistent row size and plane count to compute buffer offsets. Because the HAM row size is unvalidated and nPlanes is zero, the plugin's read loops advance beyond the bound of the allocated heap buffer. The OOB read accesses heap memory adjacent to the image data buffer. The read contents are processed as image pixel data. No direct code execution is possible from an OOB read alone (it is not a write primitive); however, the read can be used to leak heap contents if the parsed data is later reflected in output (e.g., displayed in the image viewport or saved to a re-encoded file).

Step 4 — Post-Exploitation Impact: The primary impact is a denial-of-service condition: the OOB read triggers a segmentation fault or an abort signal, crashing GIMP and losing any unsaved work. In a limited information-disclosure scenario, the attacker may exfiltrate heap memory contents (e.g., portions of other in-memory data such as clipboard contents, other open document fragments, or sensitive data that resides in heap memory adjacent to the allocation). Because the leak is heap-based and not a linear memory scan, the amount and sensitivity of disclosed data are limited. The attacker gains no remote access, no privilege escalation, and no persistence. The impact is confined to a single user session.

Impact Assessment

CVSS Rationale: The vulnerability scores 6.1 (Medium) with the vector CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H. The local attack vector (AV:L) reflects that the victim must open the file locally. Attack complexity is low: no special conditions beyond opening the file. No privileges are required (PR:N) — the victim is an unprivileged user. User interaction is required (UI:R), which is the file-open action. Scope is unchanged (S:U) — the vulnerability does not cross a trust boundary. Confidentiality impact is low (C:L) — limited heap memory disclosure with low signal-to-noise. Integrity impact is none (I:N). Availability impact is high (A:H) — the application crashes reliably.

Business Impact: For enterprise environments where GIMP is installed on user workstations, the risk is user-level: a targeted phishing email with a malicious .iff attachment can crash the application, interrupting workflows. If a heap-leak is achieved, the disclosed memory contents could include fragments of other open documents, credentials in memory, or other sensitive data processed by GIMP or allocated in the same heap arena. The confidentiality impact is low but non-zero. The lack of a patch extends the exposure window indefinitely; affected organizations must rely on mitigations.

Affected Systems & Blast Radius: All GIMP installations with the file-iff plugin are potentially affected; the plugin is part of the standard build. The blast radius is limited to a single process and a single user session per trigger. There is no evidence of remote code execution, privilege escalation, or propagation. The vulnerability does not affect other applications unless they share the file-iff code (which is internal to GIMP).

Detection Guidance

The following detection rules target behaviors and artifacts associated with attempts to exploit or with the aftermath of exploitation: the presence of suspicious IFF/ILBM files, GIMP process crashes with memory-access violations, and repeated file-open attempts on malformed files.

Sigma Rule

title: GIMP File-IFF Plugin Heap OOB Read Crash
id: 31a8fdb5-8c40-4d2a-9b8e-1c1d45f0b1a5
status: experimental
description: Detects GIMP process termination due to a crash signature consistent with the file-iff plugin heap OOB read vulnerability (CVE-2026-82324)
author: Valters IT Security
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\gimp-2.10.exe'   # adjust for GIMP versions / builds
    condition: selection and near_crash
    near_crash:
        # Windows Error Reporting (WER) events for GIMP process
        channel: Application
        EventID: 1000
        Provider_Name: 'Application Error'
        Message|contains|all:
            - 'gimp'
            - '0xc0000005'  # access violation
            - 'file-iff'
fields:
    - Image
    - CommandLine
    - Message
falsepositives:
    - Legitimate crashes due to other GIMP bugs or system instability
level: medium
tags:
    - attack.t1203
    - cve.2026-82324

YARA Rule

rule GIMP_IFF_HAM_OOB_READ_VULN
{
    meta:
        author = "Valters IT Security"
        description = "Detects IFF/ILBM files with HAM mode and zero nPlanes, indicative of CVE-2026-82324 exploitation attempts"
        cve = "CVE-2026-82324"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-82324"
    strings:
        $iff_form = "FORM" ascii
        $ilbm_chunk = "ILBM" ascii
        $ham_chunk = "HAM6" ascii or "HAM8" ascii
        $bmhd = "BMHD" ascii
        $plane_count_zero = { 00 00 00 00 }  // raw pattern; must be contextualized
    condition:
        uint32(0) == 0x4D524F46 and // 'FORM'
        $ilbm_chunk in (4..16) and
        $bmhd in (8..filesize) and
        $ham_chunk in (8..filesize) and
        // loose heuristic: BMHD chunk with zero planes is suspicious;
        // exact offset computation requires parsing the BMHD chunk
        filesize > 100
}

Suricata IDS Rule

alert http any any -> any any (msg:"GIMP CVE-2026-82324 IFF File Download Attempt"; flow:to_client,established; filemagic:"IFF data"; fileext:"iff"; content:"ILBM"; nocase; sid:9000111; rev:1; metadata:attack_target Client_Endpoint, cve CVE-2026-82324;)

This rule looks for HTTP responses carrying IFF/ILBM files being delivered to a client. It relies on Suricata's file inspection capabilities; adjust fileext for .ilbm variants. A more advanced rule would parse the BMHD chunk and alert on nPlanes == 0, but Suricata's rule language does not natively support binary structure parsing; the rule above is a network-level indicator for malicious file delivery.

Elastic Detection

// EQL rule to detect GIMP crash events on Windows via Elastic
any where process.name == "gimp-2.10.exe" and event.action == "crash" and
    // Look for specific exception codes
    exception.exception_code in ("0xc0000005", "0xc0000374") and
    // Optional: correlate with file event indicating IFF file was opened before crash
    // (requires additional data source)
    message like "*file-iff*"

Splunk SPL Query

index=windows OR index=endpoint (source="WinEventLog:Application" EventCode=1000)
    | search "gimp" AND ("0xc0000005" OR "access violation") AND "file-iff"
    | rex field=_raw "(?<process>[^\\\n]+\.exe)"
    | eval severity="medium"
    | stats count by host, process, _time
    | sort - _time
    | eval cve="CVE-2026-82324"

Wazuh OSSEC Rule

<group name="gimp,">
    <rule id="100123" level="8">
        <if_sid>5710</if_sid>  <!-- Windows application error event base -->
        <field name="win.eventdata.image">.*gimp.*</field>
        <field name="win.eventdata.exceptionCode">0xc0000005</field>
        <description>GIMP process crashed with access violation; possible CVE-2026-82324 file-iff OOB read trigger</description>
        <group>attempted_exploit,t1203,</group>
        <mitre>
            <id>T1203</id>
        </mitre>
    </rule>
</group>

Mitigation & Patch Guidance

Patch status: CVE-2026-82324 is UNPATCHED. Patch confidence is 0/4, with no patch evidence from any tracked source. No vendor advisory, no fixed version, and no workaround has been published. Until a fix is released, organizations must implement compensating controls.

1) Immediate Mitigations:

• File-extension and content filtering: Block .iff, .ilbm, and .lbm file extensions at the email gateway and web proxy. Additionally, use content inspection to detect IFF magic bytes (FORM + ILBM) and quarantine such files. This breaks the delivery chain.
• User awareness: Notify users (especially those handling graphic files) not to open IFF/ILBM files from untrusted sources. Reinforce standard phishing hygiene.
• Sandboxing: Configure endpoint security tools to launch GIMP in a sandbox or within a restricted virtualized environment if file-opening is required. This isolates a crash or a leak to the sandbox.
• Alternative software: If feasible in the short term, direct users to alternative image viewers (e.g., IrfanView, XnView) that do not include the vulnerable plugin, until GIMP releases a patch.

2) Patch / Upgrade Steps:

• Monitor GIMP release notes and advisories for a version that addresses this CVE. Apply the update as soon as it is available.
• Until a patched version exists, consider uninstalling the file-iff plugin if builds allow modular removal (specific plugin disablement paths vary by distribution). This is not a substitute for patching.

3) Long-Term Hardening:

• Application allowlisting: Use application whitelisting to ensure only approved GIMP versions execute on endpoints; block execution of unpatched versions when a patch becomes available.
• Memory-protection features: Enable ASLR, DEP/NX, and, where possible, heap integrity checks (e.g., glibc MALLOC_CHECK_) on Linux systems. These raise the cost of heap exploitation but do not prevent OOB reads.
• File-type handling policy: Restrict GIMP to handle only formats required by the business. Enforce this via group policy on Windows, and via desktop configuration on macOS/Linux.
• Monitoring: Deploy the detection rules above and tune them during a 30-day observation period to suppress false positives.
• Vendor engagement: Monitor security mailing lists (oss-security) and the GIMP issue tracker for this CVE to receive patch notifications.

References

1. NVD Entry: CVE-2026-82324 — https://nvd.nist.gov/vuln/detail/CVE-2026-82324
2. CWE-125: Out-of-bounds Read — https://cwe.mitre.org/data/definitions/125.html
3. GIMP Official Website (project) — https://www.gimp.org/
4. MITRE ATT&CK T1203: Exploitation for Client-Side Execution — https://attack.mitre.org/techniques/T1203/

Threat actor campaigns / exploit-in-the-wild evidence: None identified at the time of analysis. No public PoC exists, and CISA KEV does not list this CVE. The lack of a patch, combined with the unauthenticated remote delivery of a malicious file, makes this a candidate for future weaponization; continued monitoring is recommended.

Note on EPSS: EPSS has not yet scored this CVE; the value is not available and no estimate is provided.