CVE-2023-39318Network attack vector

Cross-site scripting via misparsed script comments

Published Sep 8, 2023 · Updated Feb 13, 2025

Cross-site scripting in Go standard library html/template before 1.20.8 and 1.21.0 allows remote attackers to inject browser scripts. The isComment check and JavaScript context transitions fail to recognize HTML-like and hashbang comments as browsers do, so template actions receive incorrect escaping. Exploitation requires an application to execute an affected template containing either comment form with attacker-controlled action data and a user to render the output.

CVSS severity6.1
Medium
EPSS probability0.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Go standard library html/template before 1.20.8 and 1.21.0 allows remote attackers to inject browser scripts. The isComment check and JavaScript context transitions fail to recognize HTML-like and hashbang comments as browsers do, so template actions receive incorrect escaping. Exploitation requires an application to execute an affected template containing either comment form with attacker-controlled action data and a user to render the output.

The record

CVE
CVE-2023-39318
Published
Sep 8, 2023
Updated
Feb 13, 2025
Vendor
Go standard library
Product
html/template
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 8, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 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 <1.20.8
  2. Affected versionversion=1.21.0-0 <1.21.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Go standard library · html/templateversion=0 <1.20.8; version=1.21.0-0 <1.21.1

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript/JScript

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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