CVE-2025-27363 in FreeType
Summary
by MITRE • 03/11/2025
An out of bounds write exists in FreeType versions 2.13.0 and below (newer versions of FreeType are not vulnerable) when attempting to parse font subglyph structures related to TrueType GX and variable font files. The vulnerable code assigns a signed short value to an unsigned long and then adds a static value causing it to wrap around and allocate too small of a heap buffer. The code then writes up to 6 signed long integers out of bounds relative to this buffer. This may result in arbitrary code execution. This vulnerability may have been exploited in the wild.
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Analysis
by VulDB Data Team • 10/27/2025
The vulnerability identified as CVE-2025-27363 represents a critical out-of-bounds write flaw within the FreeType font rendering library affecting versions 2.13.0 and earlier. This issue specifically manifests during the parsing of font subglyph structures within TrueType GX and variable font files, making it particularly dangerous in environments where diverse font formats are processed. The vulnerability stems from improper handling of data type conversions that create buffer overflow conditions, potentially enabling remote code execution. The flaw affects systems that utilize FreeType for font rendering across multiple operating systems and applications that depend on this library for text display functionality.
The technical root cause of this vulnerability lies in a problematic data type conversion pattern where a signed short value is assigned to an unsigned long variable before subsequent arithmetic operations. This conversion creates a scenario where arithmetic overflow occurs when a static value is added to the converted variable, resulting in an unexpectedly small heap buffer allocation. The buffer size calculation becomes severely compromised due to the unsigned integer wraparound behavior, creating a condition where the allocated memory is insufficient to accommodate the intended data operations. The code then proceeds to write up to six signed long integers beyond the boundaries of this inadequately sized buffer, creating a classic buffer overflow condition that can be exploited for arbitrary code execution.
The operational impact of this vulnerability extends across numerous software domains that rely on FreeType for font processing, including web browsers, office suites, graphic design applications, and operating system components. Attackers exploiting this vulnerability could potentially execute malicious code with the privileges of the affected application, leading to complete system compromise. The fact that this vulnerability may have been exploited in the wild indicates that threat actors have already developed working exploits, making immediate remediation critical for affected organizations. The vulnerability affects not only desktop environments but also mobile platforms and server applications that process font files, creating a broad attack surface.
Mitigation strategies for CVE-2025-27363 primarily focus on upgrading to FreeType versions 2.13.1 or later, where the vulnerability has been resolved through proper data type handling and buffer size calculations. Organizations should prioritize patching affected systems and applications that utilize FreeType for font rendering, particularly those processing untrusted font files from external sources. Security teams should implement monitoring for potential exploitation attempts and consider network-level controls to restrict font file processing where possible. The vulnerability aligns with CWE-121, heap-based buffer overflow, and maps to ATT&CK technique T1059.007 for remote code execution through application vulnerabilities. Additionally, input validation controls and sandboxing measures can provide additional defense-in-depth layers while awaiting full patch deployment across all affected systems.