What’s Vulnerable › Vulnerabilities

CVE-2026-39823: Bypass of meta content URL escaping causes XSS in html/template

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% 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-79

Description

CVE-2026-27142 fixed a vulnerability in which URLs were not correctly escaped inside of a <meta> tag's <content> attribute. If the URL content were to insert ASCII whitespaces around the '=' rune inside of the <content> attribute, the escaper would fail to similarly escape it, leading to XSS.

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/769920
• https://go.dev/issue/78913
• https://groups.google.com/g/golang-announce/c/qcCIEXso47M
• https://pkg.go.dev/vuln/GO-2026-4982

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