CVE-2021-26540: Apostrophe Technologies sanitize-html before 2.3.2 does not properly validate the hostnames set by the "allowe

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MEDIUM 5.3REMOTEUPGRADE

CVE-2021-26540 is a medium-severity flaw (CVSS 5.3) affecting sanitize-html. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Apostrophe Technologies sanitize-html before 2.3.2 does not properly validate the hostnames set by the "allowedIframeHostnames" option when the "allowIframeRelativeUrls" is set to true, which allows attackers to bypass hostname whitelist for iframe element, related using an src value that starts with "/\\example.com".

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.8% (top 22%)
CISA exploited list	No
Published	2021-02-08
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: apostrophecms

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-02-08 17:15 UTCPublished CVE record published
2026-06-17 03:43 UTCUpdated Record last modified

apostrophecms sanitize-html UPGRADE

Affected: < 2.3.2

Fixed in: 2.3.2

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls sanitize-html

2. UPGRADE to 2.3.2

npm install sanitize-html@">=2.3.2"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-26540?

sanitize-html: upgrade to 2.3.2. Exact commands for each OS are on this page.

Is CVE-2021-26540 being exploited?

CVE-2021-26540 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-26540 affect?

CVE-2021-26540 affects sanitize-html. Severity is medium (CVSS 5.3). Apostrophe Technologies sanitize-html before 2.3.2 does not properly validate the hostnames set by the "allowedIframeHostnames" option when the "allowIframeRelativeUrls" is set to true, which allows attackers to bypass hostname whitelist fo

How urgent is CVE-2021-26540?

Priority 48/100. Public exploit reference; Remotely exploitable, no login, no user action

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References

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