CVE-2025-57248

Executive Summary

CVE-2025-57248 is a null pointer dereference vulnerability discovered in SumatraPDF version 3.5.2. The flaw is triggered when a crafted .djvu file is opened, causing the application to crash inside libmupdf.dll within the DataPool::has_data() function. This vulnerability can lead to a denial of service (DoS) condition, potentially allowing an attacker to crash the application repeatedly. No public exploit code or patch is currently available, and the vendor's patch status is unknown.

Supply Chain & Package Security

This vulnerability does not affect NPM, PyPI, Go, or Ruby packages. It is specific to the SumatraPDF desktop application.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating insufficient data for a full assessment. However, based on the nature of the vulnerability (null pointer dereference leading to a crash), the following vector is estimated:

• Attack Vector (AV): Local (AV:L) – requires opening a malicious file.
• Attack Complexity (AC): Low (AC:L) – no special conditions.
• Privileges Required (PR): None (PR:N) – user-level interaction.
• User Interaction (UI): Required (UI:R) – user must open the file.
• Scope (S): Unchanged (S:U) – affects only the application.
• Confidentiality (C): None (C:N) – no data exposure.
• Integrity (I): None (I:N) – no data modification.
• Availability (A): High (A:H) – application 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 – Denial of Service via crafted file.

Deep Dive & Mechanics

The vulnerability resides in the DataPool::has_data() function within libmupdf.dll. When SumatraPDF processes a specially crafted .djvu file, the function attempts to access a null pointer, leading to a segmentation fault and application crash.

Root Cause: The .djvu parser fails to validate the existence of a data pool before checking its data availability. This results in a null pointer dereference.

Attack Vector: An attacker crafts a .djvu file with malformed metadata or structure that triggers the null pointer dereference. The victim must open the file using SumatraPDF 3.5.2.

Impact: Denial of service – the application crashes immediately upon opening the file. Repeated crashes can disrupt user workflow.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code path is in DataPool::has_data():

Vulnerable Code (Conceptual):

bool DataPool::has_data() {
    // No null check on data pointer
    return data->size() > 0; // data is null for crafted input
}

Patched Code (Hypothetical):

bool DataPool::has_data() {
    if (data == nullptr) {
        return false; // Safe null check
    }
    return data->size() > 0;
}

Exploitation & Lab Setup

Red Team

Objective: Crash SumatraPDF 3.5.2 on a target system.

Steps:

1. Craft a malicious .djvu file using a hex editor or fuzzing tool to trigger the null pointer dereference.
2. Deliver the file via email, download link, or USB.
3. When the victim opens the file with SumatraPDF 3.5.2, the application crashes.

Proof-of-Concept (Conceptual):

# Craft a minimal .djvu file with malformed data pool header
import struct

# Placeholder for crafted bytes
malformed_data = b'\x41\x41\x41\x41' * 100  # Example pattern
with open('exploit.djvu', 'wb') as f:
    f.write(malformed_data)

Note: No public exploit code is available. This is a conceptual example.

Blue Team

Detection:

• Monitor for crashes of SumatraPDF.exe or libmupdf.dll.
• Use file integrity monitoring to detect unusual .djvu files.
• Deploy endpoint detection and response (EDR) rules for process crashes.

Prevention:

• Block .djvu files at email gateways if not required.
• Use application whitelisting to prevent SumatraPDF execution.
• Educate users not to open untrusted .djvu files.

Indicators of Compromise (IOCs)

• File Hashes: (None available – crafted files vary)
• Process: SumatraPDF.exe crash with exception code 0xC0000005 (Access Violation)
• Module: libmupdf.dll
• Function: DataPool::has_data()
• Event Log: Windows Application Event Log – Event ID 1000 (Application Error)

Detection Engineering

YARA Rule

rule CVE_2025_57248_SumatraPDF_DJVU_Crash {
    meta:
        description = "Detects crafted .djvu files targeting CVE-2025-57248"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-57248"
    strings:
        $djvu_magic = { 41 54 26 54 }  // "AT&T" DJVU magic bytes
        $crash_pattern = { 00 00 00 00 }  // Example null pointer trigger
    condition:
        $djvu_magic at 0 and $crash_pattern
}

Sigma Rule

title: SumatraPDF Crash via Crafted DJVU File
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects application crash of SumatraPDF.exe due to null pointer dereference in libmupdf.dll
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: windows
detection:
    selection:
        EventID: 1000
        ApplicationName: SumatraPDF.exe
        FaultingModule: libmupdf.dll
        ExceptionCode: 0xc0000005
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-57248 - Potential DJVU Exploit Download"; flow:to_client,established; fileext:"djvu"; content:"|41 54 26 54|"; depth:4; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable SumatraPDF until a patch is available.
2. Use an alternative PDF/DJVU reader (e.g., Adobe Acrobat, Evince).
3. Block .djvu files at email gateways and web proxies.

Long-term:

• Monitor the vendor for a patched version.
• Apply the patch as soon as it is released.
• Implement application sandboxing to limit crash impact.

Workaround: None available.

Valters IT