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Fencer Intel
medium 6.1

CVE-2026-63670 json

ApostropheCMS: Mutation-XSS / allowedTags bypass via literal `</textarea/>` solidus close

published 2mo ago modified 19d ago also EUVD-2026-60440 , GHSA-jxwj-j7wr-gfrw

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 26%
public exploits
0
none known

Summary

ApostropheCMS is an open-source Node.js content management system. Prior to 2.17.6, sanitizeHtml() can pass disallowed executable markup through packages/sanitize-html/index.js when textarea or xmp is included in allowedTags because a literal solidus after the raw-text end-tag name is treated as text by htmlparser2 and the ontext handler emits that content without escaping, while a browser parses the following img onerror markup as active HTML. This issue is fixed in version 2.17.6.

Patch / fix

  • npm sanitize-html 2.17.6
  • apostrophecms apostrophecms 2.17.6

Is CVE-2026-63670 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
2mo ago

Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 26% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-jxwj-j7wr-gfrw referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm sanitize-html
<2.17.6
2.17.6

Affected products

  • apostrophecms apostrophe

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of apostrophecms/apostrophe published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.