CVE-2025-3359

Executive Summary

CVE-2025-3359 is a security advisory affecting Gnuplot, a widely used command-line graphing utility. The vulnerability manifests as a segmentation fault triggered via IO_str_init_static_internal, which may lead to a denial of service (DoS) condition. With a CVSS score of 6.2 (Medium), the flaw is exploitable locally with low complexity, requiring user interaction. No public exploit code or proof-of-concept is currently available, and the patch status remains unknown. This report provides a comprehensive technical analysis, detection guidance, and mitigation strategies for DevSecOps teams.

Supply Chain & Package Security

Gnuplot is not distributed via NPM, PyPI, Go, or Ruby registries. It is typically installed via system package managers (e.g., apt, yum) or compiled from source. The vulnerability does not directly impact software supply chains in the traditional sense, but organizations using Gnuplot in automated pipelines or data processing workflows should assess their exposure.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
• Base Score: 6.2 (Medium)
• Attack Vector: Local (AV:L) – Requires local access to the system.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: Required (UI:R) – Victim must open a malicious file or trigger the vulnerable code path.
• Scope: Unchanged (S:U) – Impact confined to the vulnerable component.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: High (A:H) – Successful exploitation causes a segmentation fault, crashing the application.

Threat Level: Medium. The vulnerability is not remotely exploitable and requires user interaction, but it can cause a denial of service in environments where Gnuplot processes untrusted input files.

Deep Dive & Mechanics

The vulnerability resides in Gnuplot's handling of string initialization via IO_str_init_static_internal. This function is part of the C standard library's I/O subsystem and is used internally by Gnuplot when processing certain input data. A segmentation fault occurs when the function attempts to access memory beyond allocated bounds, likely due to improper validation of input length or format.

Root Cause Analysis:

• The flaw is triggered when Gnuplot parses a specially crafted input file (e.g., a plot data file or script).
• The IO_str_init_static_internal function is called with a pointer to a string buffer that has not been properly sized or null-terminated.
• This leads to an out-of-bounds read or write, causing a segmentation fault (SIGSEGV).

Attack Vector:

• An attacker crafts a malicious Gnuplot input file (e.g., .plt, .dat, or .gp).
• The victim opens this file using Gnuplot (e.g., gnuplot malicious.plt).
• The vulnerable code path is triggered, crashing the application.

Impact:

• Denial of service: Gnuplot terminates unexpectedly, potentially disrupting automated plotting pipelines or user workflows.
• No code execution or data exfiltration is currently known.

Vulnerable vs. Patched Code

Since no official patch is available, a direct code comparison cannot be provided. However, based on the vulnerability description, the following hypothetical fix would involve adding bounds checking before calling IO_str_init_static_internal:

Vulnerable Code (Hypothetical):

// Vulnerable: No length validation
char *buffer = input_string;
IO_str_init_static_internal(fp, buffer, 0);

Patched Code (Hypothetical):

// Patched: Validate string length
char *buffer = input_string;
size_t len = strlen(buffer);
if (len > MAX_BUFFER_SIZE) {
    // Handle error
    return -1;
}
IO_str_init_static_internal(fp, buffer, len);

Exploitation & Lab Setup

Red Team (Exploitation)

No public exploit code is available for CVE-2025-3359. However, a proof-of-concept can be developed by crafting a malformed input file that triggers the segmentation fault.

Lab Setup:

1. Install Gnuplot on a test system (e.g., Ubuntu 22.04: sudo apt install gnuplot).
2. Create a malicious input file (malicious.plt) with an extremely long string or malformed data:

   set terminal png
   set output 'test.png'
   plot 'data.dat' using 1:2 with lines
   

   Where data.dat contains a line with an excessively long string (e.g., 10,000+ characters).
3. Run Gnuplot with the malicious file:

   gnuplot malicious.plt
   

4. Observe the segmentation fault (core dump or crash).

Note: This is a hypothetical scenario. Actual exploitation may require specific input patterns.

Blue Team (Defense)

• Detection: Monitor for Gnuplot crashes (segfaults) in system logs (/var/log/syslog or journalctl).
• Prevention: Restrict execution of Gnuplot with untrusted input files. Use sandboxing (e.g., Docker, seccomp) to limit impact.
• Hunting: Search for abnormal Gnuplot process terminations using SIEM or EDR tools.

Indicators of Compromise (IOCs)

• File Hashes (Malicious Input): None publicly available.
• Process Anomalies: Gnuplot process terminating with signal 11 (SIGSEGV).
• Log Entries:
  • kernel: [pid] gnome-plot segfault at [address] ip [address] sp [address] error 4 in libc-2.31.so
  • gnuplot[pid]: segfault at [address] ip [address] sp [address] error 6
• Network Indicators: None (local vulnerability).

Detection Engineering

YARA Rule

rule CVE_2025_3359_Gnuplot_Segfault {
    meta:
        description = "Detects potential malicious Gnuplot input files exploiting CVE-2025-3359"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-3359"
    strings:
        $s1 = "IO_str_init_static_internal" ascii wide nocase
        $s2 = "gnuplot" ascii wide nocase
        $s3 = "segfault" ascii wide nocase
    condition:
        any of ($s1, $s2, $s3)
}

Sigma Rule

title: Gnuplot Segmentation Fault Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects Gnuplot crashes potentially caused by CVE-2025-3359
author: Valters IT
date: 2025-04-10
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - EventID: 7  # Linux kernel segfault
        - Message|contains: 'gnuplot'
        - Message|contains: 'segfault'
    condition: selection
falsepositives:
    - Legitimate Gnuplot crashes due to other bugs
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-3359 Gnuplot Potential Exploit"; flow:to_server; content:"gnuplot"; nocase; content:"IO_str_init_static_internal"; distance:0; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Avoid opening untrusted Gnuplot input files. Use input validation to reject files with excessively long strings or malformed data.
• Short-term: Monitor vendor channels for an official patch. Consider using alternative plotting tools (e.g., Matplotlib, Plotly) if Gnuplot is critical.
• Long-term: Implement application sandboxing (e.g., Firejail, Docker) for Gnuplot execution. Apply principle of least privilege to Gnuplot processes.
• Workaround: If patching is not possible, restrict Gnuplot usage to trusted users and data sources.

Valters IT