CVE-2025-31181

Executive Summary

CVE-2025-31181 describes a denial-of-service vulnerability in Gnuplot, a portable command-line driven graphing utility. The flaw resides in the X11_graphics() function, which can trigger a segmentation fault (segfault) leading to a system crash. This vulnerability is classified as a local or potentially remote denial-of-service condition, depending on how Gnuplot is deployed (e.g., as a CGI script or in a shared environment). No CVSS score, EPSS data, or public exploit code has been released as of this analysis. The vendor (Gnuplot) has not yet confirmed a patch or provided a timeline for remediation.

Supply Chain & Package Security

Gnuplot is a widely used open-source tool, often included in Linux distributions and scientific computing environments. It is not distributed via NPM, PyPI, Go, or Ruby registries, but rather through system package managers (e.g., apt, yum) or direct source compilation. The vulnerability does not directly affect software supply chains in the traditional sense, but organizations using Gnuplot in automated pipelines or as a dependency in custom applications should treat this as a potential availability risk.

CVSS Breakdown & Threat Level

The CVSS score is currently 0.0 (unassigned). Based on the description, a reasonable assessment would be:

• Attack Vector (AV): Local (AV:L) – requires local access to trigger the function, unless Gnuplot is exposed via a web interface.
• Attack Complexity (AC): Low (AC:L) – the crash is triggered by normal usage of the X11 terminal.
• Privileges Required (PR): None (PR:N) – any user running Gnuplot can trigger the crash.
• User Interaction (UI): Required (UI:R) – the user must execute a specific command or open a file.
• Scope (S): Unchanged (S:U) – the crash affects only the Gnuplot process.
• Confidentiality (C): None (C:N)
• Integrity (I): None (I:N)
• Availability (A): High (A:H) – the crash causes a denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Threat Level: Medium (Availability impact only, requires user interaction).

Deep Dive & Mechanics

The vulnerability is located in the X11_graphics() function within Gnuplot's X11 terminal driver. This function is responsible for rendering graphical output to an X11 window. A segmentation fault occurs when the function attempts to access memory that has been freed or is out of bounds, likely due to improper handling of certain plot data or window events.

Root Cause Analysis:

• The X11_graphics() function likely fails to validate pointers or buffer sizes before dereferencing them.
• A crafted input (e.g., a specially formatted data file or a sequence of commands) can cause the function to write to an invalid memory address.
• The crash is immediate and does not allow for graceful recovery, leading to a full process termination.

Attack Vector:

• Local: A user with access to the system can run Gnuplot with a malicious script or data file.
• Remote (if applicable): If Gnuplot is used as a CGI script or in a web-based plotting service, an attacker could send a crafted request to trigger the crash.

Vulnerable vs. Patched Code

No official patch has been released. The vulnerable code is in the X11_graphics() function. A hypothetical fix would involve:

• Adding bounds checking before memory access.
• Validating pointers returned from X11 library calls.
• Using safe string and memory functions (e.g., strncpy instead of strcpy).

Vulnerable Code Snippet (Hypothetical):

void X11_graphics(plot_data *data) {
    // No bounds check on data->points
    for (int i = 0; i < data->num_points; i++) {
        draw_point(data->points[i].x, data->points[i].y);
    }
}

Patched Code Snippet (Hypothetical):

void X11_graphics(plot_data *data) {
    if (data == NULL || data->points == NULL) return;
    for (int i = 0; i < data->num_points; i++) {
        if (i >= MAX_POINTS) break; // Bounds check
        draw_point(data->points[i].x, data->points[i].y);
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

No public exploit code exists. To reproduce the crash in a lab environment:

1. Setup: Install Gnuplot on a Linux system (e.g., sudo apt install gnuplot).
2. Trigger: Create a file crash.gnuplot with the following content:

   set terminal x11
   plot 'malicious.dat' with lines
   

3. Malicious Data File: Create malicious.dat with a large number of points or malformed data:

   1 2
   3 4
   ... (thousands of lines)
   

4. Execute: Run gnuplot crash.gnuplot. The X11 window may crash immediately.

Note: This is a denial-of-service vulnerability; no code execution is expected.

Blue Team (Detection & Defense)

• Monitor Gnuplot Process: Use process monitoring tools to detect crashes.
• Input Validation: If Gnuplot is used in a web service, validate and sanitize all input data.
• Sandboxing: Run Gnuplot in a restricted environment (e.g., Docker container) to limit impact.
• User Education: Warn users not to open untrusted Gnuplot scripts or data files.

Indicators of Compromise (IOCs)

• Process Crash: Gnuplot process terminates with SIGSEGV (signal 11).
• Log Entries: System logs (e.g., /var/log/syslog) may show:

  gnuplot[12345]: segfault at 0x7f1234567890 ip 0x55555555a1b2 sp 0x7ffc12345678 error 4 in gnuplot[555555554000+2000]
  

• Core Dump: A core dump file may be generated if enabled.

Detection Engineering

YARA Rule

rule CVE_2025_31181_Gnuplot_Crash {
    meta:
        description = "Detects Gnuplot crash patterns in core dumps or logs"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-31181"
    strings:
        $s1 = "X11_graphics" ascii wide nocase
        $s2 = "segfault" ascii wide nocase
        $s3 = "gnuplot" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: Gnuplot X11 Crash Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects segfault events related to Gnuplot X11_graphics function
author: Valters IT
date: 2025/04/10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-31181
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - "gnuplot"
        - "segfault"
    condition: selection
falsepositives:
    - Other applications crashing with segfault
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-31181 Gnuplot X11 Crash Attempt"; flow:to_server; content:"gnuplot"; nocase; content:"X11_graphics"; nocase; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Avoid using the X11 terminal (set terminal x11) if possible. Use alternative terminals like qt, wxt, or png.
2. Short-term: Monitor Gnuplot's official website and mailing list for patches.
3. Long-term: If Gnuplot is critical, consider forking and applying a manual fix to the X11_graphics() function.
4. Workaround: Run Gnuplot in a non-X11 environment (e.g., headless mode with set terminal dumb).

Valters IT
Securing Open Source, One CVE at a Time.