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VulnerabilityPublished

CVE-2026-56858: Go standard library html/template · Cross-site Scripting

Affects Go standard library html/templateSource CVE Database V5

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Not known to be exploited · CVSS 6.1 Medium · fixed in 1.27.0-rc.3 : update Go standard library html/template when convenient.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score
6.1Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 24% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.27.0-rc.3, 1.26.6, 1.25.13
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 13 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

What to do

Upgrade Go standard library html/template to 1.27.0-rc.3, 1.26.6 or 1.25.13.

Affected software

ProductAffectedFixed in
Go standard libraryhtml/templateAffected
  • >=1.27.0-0 <1.27.0-rc.3
Fixed in
  • 1.27.0-rc.3
Go standard libraryhtml/templateAffected
  • >=1.26.0-0 <1.26.6
Fixed in
  • 1.26.6
Go standard libraryhtml/templateAffected
  • <1.25.13
Fixed in
  • 1.25.13
Gohtml/templatepkg:golang/html/templateOther threatsAffected
  • <1.25.13
  • >=1.26.0-0 <1.26.6
  • >=1.27.0-0 <1.27.0-rc.3
Fixed in
  • 1.25.13
  • 1.26.6
  • 1.27.0-rc.3

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

If you cannot patch yet, carefully validate and sanitize inputs before passing them to the html/template package to reduce risk.

Description

Previously, pathological inputs could close an unescaped '/' early, allowing for attack-controlled data to inject arbitrary content, potentially leading to XSS.

References

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