CVE-2025-50949

Executive Summary

CVE-2025-50949 identifies a memory leak vulnerability in FontForge version v20230101, specifically within the DlgCreate8 component. A memory leak occurs when a program fails to release allocated memory after it is no longer needed, leading to gradual resource exhaustion. Over time, this can cause the application to consume excessive system memory, potentially leading to denial of service (DoS) conditions or system instability. The vulnerability has a CVSS score of 0.0, indicating no official severity rating has been assigned, but the impact is primarily availability-related. No public exploit code or proof-of-concept is currently available, and no patch has been released by the vendor.

Supply Chain & Package Security

FontForge is a widely used open-source font editor, often integrated into software supply chains for font processing and rendering. This memory leak could affect downstream applications that rely on FontForge libraries or tools, potentially causing resource exhaustion in automated font processing pipelines. Organizations using FontForge in CI/CD workflows or server-side font rendering should monitor for updates and consider resource limits to mitigate impact.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unassigned)
• Attack Vector: Local (requires local access to trigger the leak)
• Attack Complexity: Low
• Privileges Required: Low
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: None
• Availability Impact: High (memory exhaustion can lead to DoS)
• Threat Level: Low (no public exploit, but potential for DoS in long-running processes)

Deep Dive & Mechanics

The vulnerability resides in the DlgCreate8 function, which is part of FontForge’s dialog creation subsystem. A memory leak occurs when dynamically allocated memory is not properly freed after the dialog is closed or destroyed. This can happen due to missing free() calls or improper handling of memory allocation errors. Over repeated invocations (e.g., opening and closing dialogs), the leaked memory accumulates, eventually exhausting available system memory and causing the application to crash or become unresponsive.

The leak is triggered by normal usage of the affected dialog functionality, making it a reliability issue rather than a security boundary violation. However, in environments where FontForge is used as a service or in automated scripts, an attacker with local access could repeatedly trigger the leak to cause a denial of service.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code path is identified as the DlgCreate8 function in FontForge v20230101. The fix would involve ensuring that all allocated memory blocks are freed when the dialog is destroyed, typically by adding free() calls for each allocation in the cleanup routine.

Vulnerable Code (Conceptual):

void DlgCreate8(...) {
    char *buffer = malloc(1024);
    // ... use buffer ...
    // Missing free(buffer) before return
}

Patched Code (Hypothetical):

void DlgCreate8(...) {
    char *buffer = malloc(1024);
    // ... use buffer ...
    free(buffer); // Properly free memory
}

Exploitation & Lab Setup

Red Team

No public exploit code exists for this vulnerability. To demonstrate the memory leak, an attacker could write a simple script that repeatedly opens and closes the affected dialog in FontForge, monitoring memory consumption.

Example Script (Python using subprocess):

import subprocess
import time

# Simulate repeated dialog creation
for i in range(1000):
    subprocess.run(["fontforge", "-lang=ff", "-c", "Open($1); SelectAll(); Copy()"])
    time.sleep(0.1)

Blue Team

To detect exploitation attempts, monitor for abnormal memory usage by FontForge processes. Set resource limits (e.g., using ulimit on Linux) to prevent memory exhaustion.

Detection Command:

ps aux | grep fontforge | awk '{print $2, $4, $6}'

Indicators of Compromise (IOCs)

• Process: fontforge with continuously increasing memory usage (RSS > 500 MB over time)
• Logs: System logs showing out-of-memory (OOM) killer events involving FontForge
• File: No specific file IOCs; the vulnerability is triggered via normal dialog operations

Detection Engineering

YARA Rule

rule CVE_2025_50949_Memory_Leak {
    meta:
        description = "Detects FontForge binary with potential memory leak in DlgCreate8"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50949"
    strings:
        $s1 = "DlgCreate8" ascii wide nocase
        $s2 = "fontforge" ascii wide nocase
    condition:
        $s1 and $s2
}

Sigma Rule

title: FontForge Memory Leak Detection
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects excessive memory usage by FontForge processes
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/fontforge'
        MemoryUsage: '>500000'  # RSS > 500 MB
    condition: selection
falsepositives:
    - Legitimate large font processing
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-50949 FontForge Memory Leak"; flow:to_server; content:"fontforge"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Apply resource limits (e.g., ulimit -v 1048576) to FontForge processes to prevent memory exhaustion.
• Short-term: Monitor for vendor updates or patches from the FontForge project. Consider using alternative font editors if the leak impacts critical workflows.
• Long-term: Review and fix the DlgCreate8 function in the source code to ensure proper memory deallocation. Contribute the fix upstream.

Valters IT
Securing Digital Frontiers