VulnerabilityPublished 10 Jan 2024Updated 3 Jun 2025

CVE-2023-45139: fonttools · XML External Entity (XXE)

Affects fonttoolsSource CVE Database V5

Not known to be exploited · CVSS 7.5 High : upgrade to 4.43.0 soon.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.2% chance of exploitation in 30 days – higher than 68% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.43.0

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 Jan 2024
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade fonttools to 4.43.0.

Affected software

Product	Affected	Fixed in
PyPIfonttools`pkg:pypi/fonttools`Other threats	Affected <4.43.0	Fixed in 4.43.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should take the following specific mitigation steps: 1) Immediately upgrade all instances of fontTools to version 4.43.0 or later to ensure the vulnerability is patched. 2) Audit all internal and third-party applications and services that use fontTools to identify vulnerable versions and update them accordingly. 3) Implement strict input validation and sanitization for any font files processed, especially those originating from untrusted or external sources. 4) Employ sandboxing or containerization for font processing tasks to limit the potential impact of exploitation, restricting file system and network access. 5) Monitor logs for unusual file access patterns or unexpected outbound network requests from systems running fontTools. 6) Review and tighten network egress controls to prevent unauthorized external web requests initiated by exploited hosts. 7) Educate development and security teams about the risks of XXE vulnerabilities and encourage secure coding practices when handling XML parsing. These measures go beyond generic advice by focusing on patching, environment hardening, and proactive monitoring tailored to the nature of this vulnerability.

Description

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, 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.

Impact

For European organizations, the impact of CVE-2023-45139 can be significant, especially for those relying on fontTools in their software development, font processing pipelines, or document rendering services. The vulnerability could lead to unauthorized disclosure of sensitive internal files, such as configuration files, credentials, or proprietary data, if malicious fonts are processed. Additionally, the ability to make arbitrary web requests from the host could be leveraged to pivot attacks within internal networks or exfiltrate data covertly. Organizations in sectors with strict data protection requirements, such as finance, healthcare, and government, could face compliance risks under GDPR if sensitive data is leaked. The lack of required authentication and user interaction increases the risk of automated exploitation, particularly in environments where fontTools processes fonts from untrusted sources or user uploads. Although no exploits are currently known in the wild, the high CVSS score and ease of exploitation warrant immediate attention to prevent potential attacks.

CWE-611Improper Restriction of XML External Entity Reference (opens in a new tab)
Base weaknessOWASP Top 10 A02:2025: Security Misconfiguration (opens in a new tab)
The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.
Implementation · System Configuration
Many XML parsers and validators can be configured to disable external entity expansion.
OWASP Cheat Sheets
Deserialization (opens in a new tab)
XML Security (opens in a new tab)
XML External Entity Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V5.5.2 (opens in a new tab)
Attack patterns
Data Serialization External Entities Blowup (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Jul 2025, 10:27 UTC

WeaknessesCWE-611

Technical details

References

Community reviews

Related threats