CVE-2025-66034 | fontTools is Vulnerable to Arbitrary File Write and XML injection in fontTools.varLib

Exp

fontTools is a library for manipulating fonts, written in Python. In versions from 4.33.0 to before 4.60.2, the fonttools varLib (or python3 -m fontTools.varLib) script has an arbitrary file write vulnerability that leads to remote code execution when a malicious .designspace file is processed. The vulnerability affects the main() code path of fontTools.varLib, used by the fonttools varLib CLI and any code that invokes fontTools.varLib.main(). This issue has been patched in version 4.60.2.

Published: 2025-11-28 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-66034 is rated Exploit Available (53.8/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.49%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2025-66034

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2025-66034

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.10% 0.49% +0.39%
2 2026-03-21 0.26% 0.10% -0.17%
3 2026-02-05 — 0.26% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-66034

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.3 3.1 MEDIUM
CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:L Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 1.0 4.7 [email protected]
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]

Weakness enumeration for CVE-2025-66034

GitHub Security Advisory for CVE-2025-66034

GHSA-768j-98cg-p3fv · Severity: medium · Ecosystem: pip — fontTools is Vulnerable to Arbitrary File Write and XML injection in fontTools.varLib

OS Trackers for CVE-2025-66034

vendor priority summary link
debian not yet assigned CVE-2025-66034 not yet assigned priority: Debian including 1 source packages (fonttools), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 4, open 1. https://security-tracker.debian.org/tracker/CVE-2025-66034
redhat medium — https://access.redhat.com/security/cve/CVE-2025-66034
suse medium — https://www.suse.com/security/cve/CVE-2025-66034/
ubuntu medium CVE-2025-66034 medium priority: Ubuntu including 1 source packages (fonttools), 8 status rows across 8 suites (bionic, focal, jammy, noble, plucky, questing, upstream, xenial): not-affected 4, released 4. https://ubuntu.com/security/CVE-2025-66034

Affected software / configurations for CVE-2025-66034

Vendor Product Version Raw CPE
fonttools fonttools >= 4.33.0, < 4.60.2 cpe:2.3:a:fonttools:fonttools:*:*:*:*:*:python:*:*

References for CVE-2025-66034

cvelogic Threat Intelligence