CVE-2025-23022 Overview
CVE-2025-23022 is a signed integer overflow vulnerability in FreeType 2.8.1. The flaw resides in the cf2_doFlex function within cff/cf2intrp.c, which processes Compact Font Format (CFF) Type 2 charstring Flex operators. Processing a malformed font file triggers the overflow, leading to a high-availability impact on the local system. The weakness is classified as [CWE-190] Integer Overflow or Wraparound.
Critical Impact
Local attackers can trigger a denial of service in applications that render untrusted fonts using FreeType 2.8.1.
Affected Products
- FreeType 2.8.1
- Applications and libraries embedding FreeType 2.8.1 for font rasterization
- Linux distributions shipping the unpatched FreeType 2.8.1 package
Discovery Timeline
- 2025-01-10 - CVE-2025-23022 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-23022
Vulnerability Analysis
The defect lives in cf2_doFlex, the routine that implements the CFF Type 2 flex operator used to render curves that approximate short straight lines. The function performs arithmetic on signed integer coordinates pulled from a font's charstring stack. Crafted operand values cause the signed arithmetic to wrap around, producing values outside the range expected by later drawing logic.
The overflow leads to abnormal control flow inside the CFF interpreter and crashes the process consuming the font. The CVSS vector shows only availability is affected; confidentiality and integrity remain unchanged. Exploitation requires an attacker-controlled font to be parsed by a target application such as a document viewer, browser, or shell that resolves font metadata.
Root Cause
The root cause is missing bounds validation on signed integer operands processed by cf2_doFlex in cff/cf2intrp.c. FreeType 2.8.1 does not clamp or range-check Flex coordinate arithmetic before passing values into downstream glyph outline routines. See the upstream GitLab FreeType Issue #1312 for the maintainer discussion.
Attack Vector
Exploitation is local. An attacker delivers a malicious CFF or OpenType font to the victim, and the vulnerability triggers when the FreeType-backed application parses the file. No privileges or user interaction beyond opening the crafted content are required. The Debian security team tracks distribution status in the Debian CVE-2025-23022 Tracker.
No public proof-of-concept exploit is listed in NVD, and CISA has not added the entry to the Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2025-23022
Indicators of Compromise
- Repeated crashes of font-rendering processes such as fontconfig, browsers, or document viewers when opening specific files
- Core dumps that reference cf2_doFlex or cf2intrp.c in the FreeType call stack
- Unexpected CFF/OTF font files arriving through email attachments, downloads, or embedded document resources
Detection Strategies
- Inventory installed FreeType versions across endpoints and servers to identify hosts running 2.8.1
- Audit software bills of materials (SBOMs) for third-party applications that statically link FreeType 2.8.1
- Alert on process crashes involving FreeType symbols in application error telemetry
Monitoring Recommendations
- Monitor for anomalous font files written to user profile or temp directories preceding application crashes
- Correlate application faults with recent font file access events on the same host
- Track package manager events that install or downgrade freetype to vulnerable versions
How to Mitigate CVE-2025-23022
Immediate Actions Required
- Upgrade FreeType to a fixed distribution package as tracked in the Debian CVE-2025-23022 Tracker
- Remove or replace embedded copies of FreeType 2.8.1 inside application bundles
- Restrict opening of untrusted font files, especially from email attachments and unknown websites
Patch Information
Refer to the upstream discussion in GitLab FreeType Issue #1312 and apply the fixed FreeType package provided by your operating system vendor. Rebuild any applications that statically link FreeType against a patched release.
Workarounds
- Disable automatic font loading in applications that support the option, especially browsers and document readers
- Sandbox font-rendering processes with seccomp, AppArmor, or SELinux profiles to contain crashes
- Block or quarantine untrusted CFF and OTF files at email and web gateways until patches are deployed
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
