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March 14, 2025
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How to Fix CVE-2025-27363: The Critical Out-of-Bounds Write Vulnerability in FreeType?
This article addresses CVE-2025-27363, a critical out-of-bounds write vulnerability affecting FreeType, a widely used software library for font rendering. This flaw can lead to arbitrary code execution, potentially allowing attackers to compromise systems that utilize vulnerable versions of FreeType. Security professionals in DevSecOps, application security, product security, vulnerability management, penetration testing, security operations, and engineering teams need to understand this vulnerability and take immediate steps to mitigate it. This article provides a detailed analysis of the vulnerability, its potential impact, and practical steps to remediate it. You can find more details about it on NVD.
A Short Introduction to FreeType
FreeType is a freely available software library used for rendering fonts. It supports a wide variety of font formats, including TrueType, OpenType, Type 1, CID, CFF, and others. Due to its versatility and open-source nature, FreeType is incorporated into a vast range of applications and operating systems, including desktop publishing software, web browsers, embedded systems, and mobile devices. Because it is such a common library, vulnerabilities in FreeType can have a widespread impact.
Summary of CVE-2025-27363
CVE ID: CVE-2025-27363
Description: An out-of-bounds write vulnerability exists in FreeType when parsing font subglyph structures related to TrueType GX and variable font files.
CVSS Score: 8.1 (High)
CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CVE-2025-27363 arises from a flaw in FreeType versions 2.13.0 and below when processing font subglyph structures within TrueType GX and variable font files. The vulnerability occurs because a signed short value is assigned to an unsigned long, and then a static value is added to it. This operation can cause an integer wraparound, leading to the allocation of an undersized heap buffer. Subsequently, the code writes up to six signed long integers beyond the boundaries of this buffer, resulting in an out-of-bounds write. This vulnerability is rated as high severity due to the potential for arbitrary code execution.
Impact of CVE-2025-27363
The impact of CVE-2025-27363 is significant because it could allow an attacker to execute arbitrary code on a system using a vulnerable version of FreeType. Successful exploitation could lead to complete system compromise, data theft, or denial of service. The CVSS score of 8.1 reflects the high severity and potential for significant damage. Systems rendering maliciously crafted font files are particularly at risk. Given reports suggesting potential exploitation in the wild, the urgency to address this vulnerability is heightened. Security professionals should prioritize patching or mitigating this flaw to protect their systems from potential attacks. This could mean examining systems that process font files, even indirectly through third-party software. You may also read about understanding indicator of compromise.
Products Affected by CVE-2025-27363
The following table summarizes the products affected by CVE-2025-27363:
| Product | Version(s) Affected |
|---|---|
| FreeType | <= 2.13.0 |
| Exemptions: | > 2.13.0 |
Any application or operating system using a vulnerable version of FreeType is potentially affected. This includes, but is not limited to:
Operating systems (e.g., Linux distributions with outdated FreeType packages)
Web browsers
Desktop publishing software
Office suites
Any application that renders fonts using FreeType
How to Check Your Product is Vulnerable?
To determine if your system is vulnerable, you need to identify the version of FreeType being used. Here's how:
Identify FreeType Version: The method varies depending on the operating system and application.
Linux: Use the package manager (e.g.,
dpkg -s libfreetype6on Debian/Ubuntu,rpm -q freetypeon Fedora/CentOS).Windows: Check the FreeType DLL's properties (right-click, Properties, Details tab). The DLL is commonly named
freetype.dll. Note that identifying the exact version may be difficult, depending on how the application is packaged.Applications: Consult the application's documentation or "About" section to see if the FreeType version is listed. You may need to contact the software vendor directly.
Compare to Vulnerable Versions: If the identified version is 2.13.0 or earlier, your system is vulnerable.
Indirect Dependency Analysis: For applications that bundle FreeType, use dependency scanning tools to identify bundled vulnerable versions. Many modern DevSecOps tools can identify vulnerable dependencies.
Runtime Detection (Advanced): Utilize dynamic analysis tools or debugging techniques to inspect FreeType's memory allocation behavior during font parsing. Specifically, monitor for out-of-bounds write operations when processing TrueType GX or variable font files. This approach is more complex but can confirm exploitation potential in your specific environment. As a security professional, you should also know what you should know about CVSS.
How to Fix the Vulnerabilities?
The primary remediation strategy is to update FreeType to a version beyond 2.13.0. Here's a detailed guide:
Update FreeType:
Package Managers: Use your operating system's package manager to update FreeType to the latest version. For example, on Debian/Ubuntu, use
sudo apt-get update && sudo apt-get upgrade libfreetype6. On Fedora/CentOS, usesudo dnf update freetype.Applications: If FreeType is bundled with an application, check for updates to the application itself. The application vendor is responsible for including the patched FreeType version.
Build from Source (Advanced): Download the latest FreeType source code from the official FreeType website and compile it. Replace the vulnerable FreeType library with the newly built one. This is a complex process and should be performed with caution. You can also learn about ethical hacking.
Workarounds (If Patching is Not Immediately Possible):
Network Segmentation: Isolate systems that process font files in a segmented network to limit the potential impact of a successful exploit.
Application Whitelisting: Restrict the sources from which font files can be loaded. Only allow fonts from trusted sources.
Input Validation: Implement robust input validation for font files. Check for malformed font structures or unexpected data that could trigger the vulnerability. This requires deep knowledge of font file formats.
Monitor for Suspicious Activity: Monitor network traffic and system logs for suspicious activity related to font file transfers or rendering.
Disable GX/Variable Font Support (If Feasible): If your application doesn't require TrueType GX and variable font support, consider disabling it in FreeType's configuration. This may not be possible for all applications. This will also affect support for features such as ligatures and alternate glyphs.
Monitor Official Channels: Continuously monitor official FreeType channels and security advisories for any new information or updates related to this vulnerability. One of the solutions is to have a patch management strategy.
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Arun KL
Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.
