CVE-2023-39318: Improper handling of HTML-like comments in script contexts in html/template

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-09-08 · updated 2026-06-17
Weakness: CWE-79

Description

The html/template package does not properly handle HTML-like "" comment tokens, nor hashbang "#!" comment tokens, in <script> contexts. This may cause the template parser to improperly interpret the contents of <script> contexts, causing actions to be improperly escaped. This may be leveraged to perform an XSS attack.

Affected products

Go: before 1.20.8; from 1.21.0 before 1.21.1 — fixed in 1.20.8, 1.21.1

How to fix

Upgrade to a fixed version: Go 1.20.8, 1.21.1. Check the vendor advisory for mitigations.

References

https://go.dev/cl/526156
https://go.dev/issue/62196
https://groups.google.com/g/golang-dev/c/2C5vbR-UNkI/m/L1hdrPhfBAAJ
https://pkg.go.dev/vuln/GO-2023-2041
https://security.gentoo.org/glsa/202311-09
https://security.netapp.com/advisory/ntap-20231020-0009/
https://go.dev/cl/526156
https://go.dev/issue/62196
https://groups.google.com/g/golang-dev/c/2C5vbR-UNkI/m/L1hdrPhfBAAJ
https://pkg.go.dev/vuln/GO-2023-2041
https://security.gentoo.org/glsa/202311-09
https://security.netapp.com/advisory/ntap-20231020-0009/

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