Security Resilience

CVE-2023-45139

XXE in Fonttools 4.28.2 – 4.43.0

Public PoCXXE
Published
10 January 2024
Modified
21 November 2024
Patch / advisory
View advisory
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.012 68th percentile
Risk Priority 60 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2023-45139 is a high-severity Improper Restriction of XML External Entity Reference (CWE-611) vulnerability in Fonttools Fonttools. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Data Obfuscation (T1001); ranked in the top 32% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to CM-6 (Configuration Settings) and SA-11 (Developer Testing and Evaluation) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A02:2025 Security Misconfiguration

EU & UK References

Vulnerability Data

fontTools is a library for manipulating fonts, written in Python. The subsetting module has a XML External Entity Injection (XXE) vulnerability which allows an attacker to resolve arbitrary entities when a candidate font (OT-SVG fonts), which contains a SVG table,…

more

is parsed. This allows attackers to include arbitrary files from the filesystem fontTools is running on or make web requests from the host system. This vulnerability has been patched in version 4.43.0.

CWE(s)
CWE-611

Related Threats

MITRE ATT&CK Enterprise Techniques

T1001 Data Obfuscation Command And Control
Adversaries may obfuscate command and control traffic to make it more difficult to detect.
attack.mitre.org →
T1003 OS Credential Dumping Credential Access
Adversaries may attempt to dump credentials to obtain account login and credential material, normally in the form of a hash or a clear text password.
attack.mitre.org →
T1003.001 LSASS Memory Credential Access
Adversaries may attempt to access credential material stored in the process memory of the Local Security Authority Subsystem Service (LSASS).
attack.mitre.org →
T1003.006 DCSync Credential Access
Adversaries may attempt to access credentials and other sensitive information by abusing a Windows Domain Controller's application programming interface (API)(Citation: Microsoft DRSR Dec 2017) (Citation: Microsoft GetNCCChanges) (Citati…
attack.mitre.org →
T1003.007 Proc Filesystem Credential Access
Adversaries may gather credentials from the proc filesystem or `/proc`.
attack.mitre.org →
T1005 Data from Local System Collection
Adversaries may search local system sources, such as file systems, configuration files, local databases, virtual machine files, or process memory, to find files of interest and sensitive data prior to Exfiltration.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-66034Same product: Fonttools Fonttools
CVE-2024-12476Shared CWE-611
CVE-2023-26999Shared CWE-611
CVE-2026-88789Shared CWE-611
CVE-2024-1167Shared CWE-611
CVE-2024-52800Shared CWE-611
CVE-2025-2775Shared CWE-611
CVE-2025-27523Shared CWE-611
CVE-2023-20173Shared CWE-611
CVE-2025-66370Shared CWE-611

Affected Assets

fonttools
fonttools
4.28.2 — 4.43.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.5.1
  • V15.3.2

Mitigating Controls (NIST 800-53 r5) AI

CM-6 Configuration Settings good match

Secure configuration settings can disable external entity processing in XML parsers.

SA-11 Developer Testing and Evaluation good match

Developer testing can discover XXE flaws through targeted XML parsing tests.

SI-10 Information Input Validation good match

Input validation can reject or sanitize XML containing external entity references.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

ID.RA-01 partial match
blocks

Vulnerability scanning can discover XXE flaws but does not prevent their introduction in code.

PR.PS-01 partial match
blocks

Hardened XML parser configurations directly disable external entity resolution.

PR.PS-02 partial match
blocks

Patching eliminates XXE-vulnerable parser versions but is only one aspect of software maintenance.

PR.PS-06 partial match
blocks

Secure SDLC practices include input validation and safe XML parser configuration that prevent XXE.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.14 Information transfer partial match
removes
A.5.15 Access control partial match
removes
A.5.16 Identity management partial match
removes
A.5.17 Authentication information partial match
removes
A.5.18 Access rights partial match
removes
A.5.32 Intellectual property rights partial match
removes

References