CVE-2019-18224 – CVE-2019-18224 is a critical heap-based buffer ... (How to Fix)

Q: What is the severity of CVE-2019-18224?

CVE-2019-18224 has a CVSS score of 9.8 (CRITICAL). CVE-2019-18224 is a critical heap-based buffer overflow vulnerability in GNU libidn2's idn2_to_ascii_4i function. Attackers can exploit this by providing a specially crafted long domain string, potentially leading to remote code execution or denial of service. This affects any system or application using vulnerable versions of libidn2 for Internationalized Domain Name processing.

📋 TL;DR

CVE-2019-18224 is a critical heap-based buffer overflow vulnerability in GNU libidn2's idn2_to_ascii_4i function. Attackers can exploit this by providing a specially crafted long domain string, potentially leading to remote code execution or denial of service. This affects any system or application using vulnerable versions of libidn2 for Internationalized Domain Name processing.

💻 Affected Systems

Products:

GNU libidn2

Versions: All versions before 2.1.1

Operating Systems: Linux, Unix-like systems

Default Config Vulnerable: ⚠️ Yes

Notes: Any application linking against vulnerable libidn2 versions is affected when processing domain names.

📦 What is this software?

Libidn2 by Gnu

View all CVEs affecting Libidn2 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with full system compromise, allowing attackers to execute arbitrary code with the privileges of the vulnerable process.

🟠

Likely Case

Denial of service through application crashes or system instability, potentially leading to service disruption.

🟢

If Mitigated

Limited impact if proper memory protection mechanisms (ASLR, DEP) are in place, though crashes may still occur.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

The vulnerability is triggered by simple long domain strings, making exploitation straightforward. Public proof-of-concept exists in the OSS-Fuzz bug report.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 2.1.1

Vendor Advisory: https://github.com/libidn/libidn2/commit/e4d1558aa2c1c04a05066ee8600f37603890ba8c

Restart Required: Yes

Instructions:

1. Update libidn2 to version 2.1.1 or later using your distribution's package manager. 2. For source installations: download from https://ftp.gnu.org/gnu/libidn/ and compile. 3. Restart affected services or applications using libidn2.

🔧 Temporary Workarounds

Input validation

all

Implement strict length validation for domain names before passing to libidn2 functions.

🧯 If You Can't Patch

Implement network filtering to block unusually long domain names at perimeter devices.
Use application-level input validation to reject domain names exceeding reasonable length limits.

🔍 How to Verify

Check if Vulnerable:

Check libidn2 version: `ldconfig -p | grep libidn2` and compare with version 2.1.1.

Check Version:

pkg-config --modversion libidn2 2>/dev/null || ldconfig -p | grep libidn2

Verify Fix Applied:

Verify installed version is 2.1.1 or higher: `pkg-config --modversion libidn2` or check package manager.

📡 Detection & Monitoring

Log Indicators:

Application crashes with segmentation faults
Memory corruption errors in system logs
Unusual process termination

Network Indicators:

Requests with unusually long domain names
DNS queries with excessive length

SIEM Query:

source="*syslog*" AND ("segmentation fault" OR "buffer overflow") AND process="*libidn2*"

📊 Metadata

CVE ID: CVE-2019-18224

CVSS v3 Score: 9.8 (CRITICAL)

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

CWE: CWE-787

Published: October 21, 2019

Last Updated: November 21, 2024

🔗 References

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

If you're affected by CVE-2019-18224, you might also want to check these: