CVE-2026-39823 Bypass of meta content URL escaping causes XSS in html/template
Attackers can execute arbitrary scripts by bypassing URL escaping in meta content attributes within Go's html/template package.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-39823?
CVE-2026-39823 is a medium-severity cross-site scripting vulnerability in Golang Go, published on 7 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-39823?
2 open source packages ship an affected version, including golang and stdlib. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
golang Bitnami | All versions | 1.25.10, 1.26.3 |
stdlib Go | All versions | 1.25.10, 1.26.3 |
Products include Golang Go.
How do I fix CVE-2026-39823?
Upgrade golang to a fixed version for your release line: 1.25.10 or 1.26.3.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-39823 being exploited?
There is no known exploitation of CVE-2026-39823 in the wild and no public exploit code.
Other vulnerabilities in Golang Go
- CVE-2020-0601 Microsoft Windows CryptoAPI Spoofing
- CVE-2026-27143 Missing bound checks can lead to memory corruption in safe Go in cmd/compile
- CVE-2024-24790 Unexpected behavior from Is methods for IPv4-mapped IPv6 addresses in net/netip
- CVE-2023-39320 Arbitrary code execution via go.mod toolchain directive in cmd/go
- CVE-2023-24540 Improper handling of JavaScript whitespace in html/template
Sources
Also known as AZL-98700, BELL-CVE-2026-39823, BIT-golang-2026-39823, CLEANSTART-2026-EF65373, CLEANSTART-2026-FK00511, CLEANSTART-2026-FZ40980 and 795 more.