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CVE-2021-26540

19
FAUCET Score

CVE-2021-26540 describes a vulnerability in Apostrophe Technologies' sanitize-html library, affecting versions prior to 2.3.2. This flaw allows attackers to bypass hostname whitelisting for iframe elements when the "allowIframeRelativeUrls" option is enabled, by crafting specific relative URLs. Rated as Medium severity (CVSS 5.3), it has a low impact on integrity and requires no user interaction or privileges to exploit. There is currently no evidence of active exploitation, public exploit code, or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
< 2.3.2CPE matchmatch criteria
cpe:2.3:a:apostrophecms:sanitize-html:*:*:*:*:*:node.js:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.75%
Probability of exploitation in next 30 days
EPSS Percentile
75.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0175 is in the 62nd percentile among its peer group of 23,705 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (6)

github_advisorypatch availablevia nvd_reference
View patch
npmpatch availablevia ghsa
Product: sanitize-htmlFixed in: 2.3.2
redhatpatch availablevia redhat_api
Product: Red Hat OpenShift Container Platform 4.8Fixed in: openshift4/ose-console:v4.8.0-202107010336.p0.git.188a490.assembly.stream
View patch
redhatpatch availablevia redhat_api
Product: Red Hat OpenShift Container Platform 4.8Fixed in: openshift4/ose-thanos-rhel8:v4.8.0-202106291913.p0.git.c358e96.assembly.stream
View patch
redhatpatch availablevia redhat_api
Product: Red Hat OpenShift Container Platform 4.9Fixed in: openshift4/ose-prometheus:v4.9.0-202109302016.p0.git.3197fa7.assembly.stream
View patch
redhatno patchvia redhat_api
Product: OpenShift Service Mesh 2.0Fixed in: servicemesh-prometheus

Vendor Advisories (2)

npmGHSA-mjxr-4v3x-q3m4medium

Improper Input Validation in sanitize-html

May 6, 2021
redhatCVE-2021-26540Moderate

sanitize-html: improper validation of hostnames set by the "allowedIframeHostnames" option can lead to bypass hostname whitelist for iframe element

Jan 26, 2021

References

advisory.checkmarx.net / advisory/CX-2021-4309
ExploitPatchThird Party Advisory
github.com / apostrophecms/sanitize-html/blob/main/CHANGELOG.md
Release NotesThird Party Advisory
github.com / apostrophecms/sanitize-html/pull/460
PatchThird Party Advisory