CVE-2025-27836

Executive Summary

CVE-2025-27836 is a buffer overflow vulnerability in Artifex Ghostscript, specifically within the BJ10V device driver located in contrib/japanese/gdev10v.c. The flaw allows an attacker to cause a print buffer overflow, potentially leading to arbitrary code execution or denial of service. The vulnerability affects all versions of Ghostscript before 10.05.0. No public proof-of-concept (PoC) or exploit code is currently available, and the CVSS score is listed as 0.0 due to incomplete scoring data. The EPSS score is 0.0%, indicating a low probability of exploitation in the wild at this time. However, given the widespread use of Ghostscript in document processing pipelines, this vulnerability poses a significant risk to systems that process untrusted PostScript or PDF files.

Supply Chain & Package Security

Ghostscript is a critical component in many Linux distributions and document processing systems. It is often used as a backend for printing, PDF generation, and image processing. The vulnerability in the BJ10V device driver could be exploited by an attacker who can supply a malicious PostScript file to a vulnerable Ghostscript instance. This could occur through web applications that allow file uploads, email gateways, or any service that processes documents. Organizations should audit their use of Ghostscript and ensure that all instances are updated to version 10.05.0 or later.

CVSS Breakdown & Threat Level

The CVSS score for CVE-2025-27836 is currently listed as 0.0, which is likely a placeholder due to incomplete scoring data from the NVD. Based on the nature of the vulnerability (buffer overflow in a device driver), a reasonable CVSS v3.1 vector would be:

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

• Attack Vector (AV): Local (L) – The attacker must provide a malicious file to the local system.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication is needed.
• User Interaction (UI): Required (R) – The victim must open or process the malicious file.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): High (H) – Potential for data exfiltration.
• Integrity (I): High (H) – Potential for file modification.
• Availability (A): High (H) – Potential for denial of service.

Threat Level: High. Although no public exploit exists, the vulnerability is in a widely used library and could be weaponized.

Deep Dive & Mechanics

The vulnerability resides in the BJ10V device driver, which is part of the Japanese language support in Ghostscript. The gdev10v.c file contains a function that handles print buffer operations. A buffer overflow occurs when the driver writes data beyond the allocated buffer size, likely due to insufficient bounds checking when processing specially crafted PostScript commands.

The BJ10V device is a printer driver for Canon BJ-10v printers. When Ghostscript processes a PostScript file that targets this device, it allocates a buffer for the print data. If the input data exceeds the buffer size, the overflow can corrupt adjacent memory, potentially allowing an attacker to overwrite function pointers or other critical data structures.

The vulnerability is triggered by providing a malicious PostScript file that specifies a large amount of data for the BJ10V device. The lack of proper validation in the buffer handling code leads to the overflow.

Vulnerable vs. Patched Code

The vulnerable code is in contrib/japanese/gdev10v.c. The exact fix is not publicly available, but the patch likely involves adding bounds checking to the buffer write operations.

Vulnerable Code (Conceptual):

// In gdev10v.c
static int bj10v_print_page(gx_device_printer *pdev, FILE *prn_stream) {
    char buffer[1024];
    // ... read data into buffer without checking size ...
    while (fgets(buffer, sizeof(buffer), prn_stream) != NULL) {
        // Process data
    }
}

Patched Code (Conceptual):

// In gdev10v.c
static int bj10v_print_page(gx_device_printer *pdev, FILE *prn_stream) {
    char buffer[1024];
    // ... read data into buffer with size check ...
    while (fgets(buffer, sizeof(buffer), prn_stream) != NULL) {
        if (strlen(buffer) >= sizeof(buffer)) {
            // Handle overflow
            break;
        }
        // Process data
    }
}

The patch ensures that the buffer is not overflowed by limiting the amount of data read.

Exploitation & Lab Setup

Red Team

Objective: Exploit the buffer overflow to achieve arbitrary code execution.

Lab Setup:

1. Install a vulnerable version of Ghostscript (e.g., 10.04.0) on a test system.
2. Create a malicious PostScript file that triggers the overflow.

Exploit Steps:

1. Craft a PostScript file that sets the device to BJ10V and sends a large amount of data.
2. Use a tool like gs to process the file:

   gs -sDEVICE=bj10v -o output.bmp exploit.ps
   

3. The overflow may cause a crash or allow code execution if the attacker can control the overflowed data.

Note: No public exploit code is available. This is a theoretical approach.

Blue Team

Objective: Detect and prevent exploitation.

Detection:

1. Monitor for crashes or abnormal behavior in Ghostscript processes.
2. Use file scanning to detect malicious PostScript files.
3. Implement network segmentation to limit exposure.

Prevention:

1. Upgrade to Ghostscript 10.05.0 or later.
2. Use application whitelisting to restrict which applications can process PostScript files.
3. Deploy intrusion detection systems (IDS) to monitor for exploit attempts.

Indicators of Compromise (IOCs)

• File Hashes: No specific hashes available.
• Network Indicators: Unusual PostScript files being processed.
• System Indicators: Ghostscript crashes or segmentation faults.
• Log Entries: Errors in Ghostscript logs related to buffer overflow.

Detection Engineering

YARA Rule

rule CVE_2025_27836_Ghostscript_BJ10V_Overflow {
    meta:
        description = "Detects malicious PostScript files targeting CVE-2025-27836"
        author = "Valters IT"
        date = "2025-03-01"
        reference = "CVE-2025-27836"
    strings:
        $bj10v = "bj10v" nocase
        $overflow = "buffer" nocase
    condition:
        $bj10v and $overflow
}

Sigma Rule

title: Ghostscript BJ10V Buffer Overflow Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2025-27836 in Ghostscript
author: Valters IT
date: 2025-03-01
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\gs.exe'
        CommandLine|contains: 'bj10v'
    condition: selection
falsepositives:
    - Legitimate use of BJ10V device
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-27836 Ghostscript BJ10V Buffer Overflow Attempt"; flow:to_server,established; content:"bj10v"; nocase; content:"buffer"; nocase; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade Ghostscript to version 10.05.0 or later.
2. Workaround: If upgrading is not possible, disable the BJ10V device driver by removing or renaming the gdev10v.c file (not recommended).
3. Long-term: Implement a robust patch management process for all software components.
4. Monitoring: Deploy the detection rules provided above to identify exploitation attempts.
5. User Education: Train users to avoid opening untrusted PostScript or PDF files.

Valters IT
Securing Digital Frontiers