CVE-2023-24539

HTML injection via permissive CSS value filtering

Published May 11, 2023 · Updated Jan 24, 2025

HTML injection in Go standard library html/template before 1.19.9 and 1.20.0 through 1.20.3 allows attackers to inject unexpected HTML. The cssValueFilter function accepts angle brackets in CSS values, so slash-separated template actions can close the surrounding CSS context. Exploitation requires an application to execute the affected template pattern with untrusted input, and the resulting markup is emitted into its HTML output.

CVSS severity7.3
High
EPSS probability1.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTML injection in Go standard library html/template before 1.19.9 and 1.20.0 through 1.20.3 allows attackers to inject unexpected HTML. The cssValueFilter function accepts angle brackets in CSS values, so slash-separated template actions can close the surrounding CSS context. Exploitation requires an application to execute the affected template pattern with untrusted input, and the resulting markup is emitted into its HTML output.

The record

CVE
CVE-2023-24539
Published
May 11, 2023
Updated
Jan 24, 2025
Vendor
Go standard library
Product
html/template
Classifications
CWE-94
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. May 11, 2023CVE publishedPublication date reported by the CVE source.
  2. Jan 24, 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=0 <1.19.9
  2. Affected versionversion=1.20.0-0 <1.20.4

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Go standard library · html/templateversion=0 <1.19.9; version=1.20.0-0 <1.20.4

Published CVSS scores

7.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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