CVE-2021-21366: xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module

Routine

MEDIUM 4.3WATCHLISTUPGRADEMITIGATE

CVE-2021-21366 is a medium-severity flaw (CVSS 4.3) affecting xmldom, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. xmldom versions 0.4.0 and older do not correctly preserve system identifiers, FPIs or namespaces when repeatedly parsing and serializing maliciously crafted documents. This may lead to unexpected syntactic changes during XML processing in some downstream applications. This is fixed in version 0.5.0. As a workaround downstream applications can

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.3% (top 29%)
CISA exploited list	No
Weakness	CWE-115, CWE-436
Published	2021-03-12
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: debian · xmldom project

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

Am I affected?

Timeline

2021-03-12 17:15 UTCPublished CVE record published
2026-06-17 03:35 UTCUpdated Record last modified

xmldom project xmldom UPGRADE

Affected: < 0.5.0

Fixed in: 0.5.0

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls xmldom

2. UPGRADE to 0.5.0

npm install xmldom@">=0.5.0"

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2021-21366?

xmldom: upgrade to 0.5.0; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-21366 being exploited?

CVE-2021-21366 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-2021-21366 affect?

CVE-2021-21366 affects xmldom, debian linux. Severity is medium (CVSS 4.3). xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. xmldom versions 0.4.0 and older do not correctly preserve system identifiers, FPIs or namespaces when repeatedly parsing and serializi

How urgent is CVE-2021-21366?

Priority 38/100. On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2022-37616 CRITICAL 9.8 UPGRADE MITIGATE A prototype pollution vulnerability exists in the function copy in dom.js in the xmldom (published as @xmldom/
CVE-2021-32796 MEDIUM 6.5 UPGRADE xmldom is an open source pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer

References

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