CVE-2026-39826: Escaper bypass leads to XSS in html/template

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-07 · updated 2026-10-26
Weakness: CWE-116

Description

If a trusted template author were to write a <script> tag containing an empty 'type' attribute or a 'type' attribute with an ASCII whitespace, the execution of the template would incorrectly escape any data passed into the <script> block.

Affected products

Go: before 1.25.10; from 1.26.0 before 1.26.3 — fixed in 1.25.10, 1.26.3
Go Stdlib: before 1.25.10; from 1.26.0-0 before 1.26.3 — fixed in 1.25.10, 1.26.3

How to fix

Upgrade to a fixed version: Go 1.25.10, 1.26.3; Go Stdlib 1.25.10, 1.26.3. Check the vendor advisory for mitigations.

References

https://go.dev/cl/771180
https://go.dev/issue/78981
https://groups.google.com/g/golang-announce/c/qcCIEXso47M
https://pkg.go.dev/vuln/GO-2026-4980

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