How severe is CVE-2021-26540?

CVE-2021-26540 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2021-26540 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26540?

CVE-2021-26540 affects Apostrophecms Sanitize-html. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-26540?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-26540 published?

CVE-2021-26540 was published on 2021-02-08 and last updated on 2026-06-17.

CVE-2021-26540

CVE-2021-26540 is a medium-severity vulnerability in Apostrophecms Sanitize-html with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 2% (75th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Apostrophecms Sanitize-html
Published: 2021-02-08
Last modified: 2026-06-17

Description

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".

Frequently asked questions

What is CVE-2021-26540?: 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".
How severe is CVE-2021-26540?: CVE-2021-26540 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2021-26540 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26540?: CVE-2021-26540 affects Apostrophecms Sanitize-html. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-26540?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-26540 published?: CVE-2021-26540 was published on 2021-02-08 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:apostrophecms:sanitize-html:*:*:*:*:*:node.js:*:*

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