CVE-2025-31178

Executive Summary

CVE-2025-31178 describes a NULL pointer dereference vulnerability in the GetAnnotateString() function of Gnuplot, a widely used command-line graphing utility. This flaw can lead to a segmentation fault (segfault) and cause a system crash when processing specially crafted input. The vulnerability is currently unpatched, and no public exploit code or proof-of-concept (PoC) is available. The CVSS score is 0.0, indicating insufficient data for scoring, but the impact is a denial-of-service (DoS) condition. This report provides a deep technical analysis, detection strategies, and mitigation recommendations.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD) – No vector assigned due to lack of details.
• Threat Level: Medium (estimated) – Denial-of-service via crash, no remote code execution confirmed.
• Attack Vector: Likely local or via crafted input file (e.g., .plt script).
• Impact: System crash (segmentation fault) of the Gnuplot process.

Deep Dive & Mechanics

The vulnerability resides in the GetAnnotateString() function within Gnuplot's source code. This function is responsible for parsing and handling annotation strings (e.g., labels, titles) in plot commands. A NULL pointer dereference occurs when the function attempts to access memory through a pointer that has not been properly initialized or has been set to NULL. This typically happens when:

1. An attacker provides a malformed input file or command string.
2. The function fails to validate the pointer before dereferencing it.
3. The operating system sends a SIGSEGV signal, terminating the process.

The exact trigger mechanism is unknown, but it likely involves a specific sequence of characters or a missing argument in an annotation command. The crash is immediate and does not allow for code execution unless combined with other vulnerabilities.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code path is in the GetAnnotateString() function. A patched version would include a NULL check before dereferencing the pointer.

Vulnerable Code (pseudocode):

char* GetAnnotateString(char* input) {
    char* result = parse_annotation(input);
    // No NULL check
    return result;
}

Patched Code (pseudocode):

char* GetAnnotateString(char* input) {
    char* result = parse_annotation(input);
    if (result == NULL) {
        return NULL; // or handle error
    }
    return result;
}

Exploitation & Lab Setup

Red Team

Objective: Trigger a denial-of-service condition on a target system running Gnuplot.

Lab Setup:

• Target: Ubuntu 22.04 with Gnuplot 5.4.1 installed.
• Attacker: Kali Linux with crafted input file.

Steps:

1. Create a malicious Gnuplot script (exploit.plt) that triggers the NULL pointer dereference.
2. Execute the script on the target: gnuplot exploit.plt
3. Observe the segmentation fault and crash.

Example Malicious Script (hypothetical):

# exploit.plt
set title ""
set label 1 at 0,0 ""
plot sin(x)

Note: No public PoC exists; this is a theoretical example.

Blue Team

Objective: Detect and prevent exploitation attempts.

Detection:

• Monitor for Gnuplot crashes (segfaults) in system logs.
• Use file integrity monitoring to detect malicious .plt files.
• Implement input validation for Gnuplot scripts.

Prevention:

• Restrict execution of Gnuplot to trusted users.
• Use AppArmor or SELinux to confine Gnuplot.
• Apply vendor patches when available.

Indicators of Compromise (IOCs)

• File Hashes: None available (no PoC).
• Process Anomalies: Gnuplot process crashes with SIGSEGV.
• Log Entries:
  • /var/log/syslog: gnuplot[PID]: segfault at ADDRESS ip IP sp SP error 6 in gnuplot
  • /var/log/kern.log: gnuplot[PID]: segfault at ADDRESS ip IP sp SP error 6 in gnuplot
• Network Traffic: None (local vulnerability).

Detection Engineering

YARA Rule

rule CVE_2025_31178_Gnuplot_AnnotateString {
    meta:
        description = "Detects Gnuplot scripts that may trigger CVE-2025-31178"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-31178"
    strings:
        $s1 = "set label" nocase
        $s2 = "set title" nocase
        $s3 = "set arrow" nocase
    condition:
        any of ($s*) and filesize < 10KB
}

Sigma Rule

title: Gnuplot Segmentation Fault Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects Gnuplot crashes due to CVE-2025-31178
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - EventID: 7 (Linux Syslog)
        - Message: "*segfault*gnuplot*"
    condition: selection
falsepositives:
    - Legitimate Gnuplot crashes due to other bugs
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-31178 Gnuplot AnnotateString DoS Attempt"; flow:to_server; content:"gnuplot"; nocase; content:"set label"; nocase; within:100; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Patch: No official patch available. Monitor the Gnuplot project for updates.
2. Workaround: Avoid processing untrusted Gnuplot scripts. Use input validation.
3. Mitigation:
   • Restrict Gnuplot execution to trusted users.
   • Use a sandbox (e.g., Docker, Firejail) to run Gnuplot.
   • Apply system-level protections (ASLR, NX).
4. Detection: Implement the YARA, Sigma, and Suricata rules above.
5. Monitoring: Enable logging for segfaults and monitor for anomalies.

Valters IT
Securing your digital frontier.