CVE-2025-66034Public exploit

Code execution via unsanitized designspace output paths

Published Nov 29, 2025 · Updated Dec 1, 2025

Arbitrary file write in FontTools fontTools 4.33.0 through 4.60.1 allows context-dependent attackers to execute code via a crafted .designspace file. In fontTools.varLib.main(), each variable-font filename is joined to the output directory without reducing it to a basename, while labelname content is serialized into the generated file. A user or automated process must invoke the affected path on the crafted file; code execution also requires the written payload to reach an executable context.

CVSS severity6.3
Medium
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Arbitrary file write in FontTools fontTools 4.33.0 through 4.60.1 allows context-dependent attackers to execute code via a crafted .designspace file. In fontTools.varLib.main(), each variable-font filename is joined to the output directory without reducing it to a basename, while labelname content is serialized into the generated file. A user or automated process must invoke the affected path on the crafted file; code execution also requires the written payload to reach an executable context.

The record

CVE
CVE-2025-66034
Published
Nov 29, 2025
Updated
Dec 1, 2025
Vendor
FontTools
Product
fontTools
Classifications
CWE-91, T1203, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 29, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 1, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 4.33.0, < 4.60.2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

FontTools · fontToolsversion=>= 4.33.0, < 4.60.2

Published CVSS scores

6.3GitHub Maintainer Security AdvisoryCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-91XML Injection (aka Blind XPath Injection)
T1203Exploitation for Client Execution
T1204.002Malicious File

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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