CVE-2025-66034
Description
This vulnerability in fontTools varLib allows a crafted .designspace file to trigger arbitrary file writes and XML-based content injection during variable-font generation. Because filenames are not sanitized, an attacker can use path traversal to overwrite files anywhere on the filesystem, and malicious payloads embedded in XML labelname elements can be injected directly into the generated output. When these overwritten files reside in executable or web-served locations, this can enable local remote-code execution or corruption of application or configuration files. The issue affects the varLib CLI and any code that invokes fontTools.varLib.main().
Statement
This issue is rated Moderate rather than Important because the exploitability hinges on several limiting technical factors despite the high integrity impact. The arbitrary file-write and XML-injection pathways are only reachable when a user or automated workflow locally processes a malicious .designspace file, giving the flaw a local attack vector (AV:L) and requiring explicit user interaction (UI:R)—meaning an attacker cannot trigger it remotely over the network. The attack also involves high complexity (AC:H), as it depends on crafted designspace structures, controlled font sources, and specific invocation of fonttools varLib or code that directly calls varLib.main(). Additionally, the vulnerability does not expose confidentiality, and availability effects are limited to potential file corruption. These constraints significantly narrow real-world exposure, keeping the risk profile in the Moderate range despite the possibility of high local integrity impact when exploited.
Mitigation
To mitigate this issue, avoid processing untrusted .designspace files with the fontTools varLib script or any application that invokes fontTools.varLib.main(). Restrict the execution environment of processes handling .designspace files to minimize potential impact from arbitrary file writes. If the fonttools package is not required, consider removing it.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.3 | 9.8 | 6.3 |
| Attack Vector | Local | Network | Local |
| Attack Complexity | High | Low | High |
| Privileges Required | None | None | None |
| User Interaction | Required | None | Required |
| Scope | Changed | Unchanged | Changed |
| Confidentiality | None | High | None |
| Integrity Impact | High | High | High |
| Availability Impact | Low | High | Low |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:L
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:L
Understanding the Weakness (CWE)
Confidentiality,Integrity,Availability
Technical Impact: Execute Unauthorized Code or Commands; Read Application Data; Modify Application Data
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