Medium

XSS in Go html/template meta refresh content attribute escaping

IdentifiersCVE-2026-27142CWE-79· Improper Neutralization of Input…

CVE-2026-27142 affects Go's html/template package. Actions that insert URLs into the content attribute of HTML meta tags were not properly escaped. In the specific case where the meta tag also includes http-equiv="refresh", the browser interprets the content attribute as a refresh directive containing a URL, and the missing escaping can permit attacker-controlled input to break out of the intended context and trigger cross-site scripting. The issue was fixed in the Go 1.26.1 / 1.25.8 security releases. The Go project also introduced a GODEBUG setting, htmlmetacontenturlescape, related to this escaping behavior; setting htmlmetacontenturlescape=0 disables the new escaping behavior for compatibility.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can result in cross-site scripting in applications that render untrusted data into the content attribute of a meta tag used for HTTP refresh behavior. This can enable execution of attacker-controlled script in the victim's browser in the security context of the affected application, with the usual downstream impacts of XSS such as session theft, request forgery, DOM manipulation, credential capture, or delivery of further client-side payloads.

Mitigation

If you can’t patch tonight, do this now.

As an interim mitigation, avoid placing untrusted or user-controlled data into the content attribute of meta tags, especially meta tags using http-equiv="refresh". If application behavior permits, remove or disable meta refresh usage and perform redirects server-side instead. Review templates for dynamic values rendered into meta content attributes and constrain them to trusted, validated URLs. Note that the GODEBUG setting htmlmetacontenturlescape=0 disables the protective escaping and should not be used as a security mitigation.

Remediation

Patch, then assume compromise.

Upgrade the Go toolchain to a fixed release that includes the html/template correction, specifically Go 1.26.1, Go 1.25.8, or later. Rebuild and redeploy affected applications with the updated toolchain so templates are generated with the corrected escaping behavior. Avoid relying on the compatibility toggle except as a temporary measure during migration.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

GolangGoapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

17 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

17 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity17

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-27142

NVD

nvd.nist.gov/vuln/detail/CVE-2026-27142

MITRE CWE · CWE-79

Improper Neutralization of Input During Web…

Vendor Advisory

pkg.go.dev/vuln/GO-2026-4603

Release Notes

groups.google.com/g/golang-announce/c/EdhZqrQ98hk