CVE-2021-21366 [Medium] | Security Vulnerability in Xmldom

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 validate the input and reject the maliciously crafted documents.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-17	1.43%	1.33%	-0.10%
2	2026-06-15	1.34%	1.43%	+0.09%
3	2026-05-27	—	1.34%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-17

1.43%

1.33%

-0.10%

2026-06-15

1.34%

1.43%

+0.09%

2026-05-27

—

1.34%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
4.3	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	2.8	1.4	[email protected]
4.3	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	2.8	1.4	[email protected]
4.3	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:N/I:P/A:N` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:M) Exploitation needs some favorable conditions, but not exceptional ones. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:N) No availability impact.	8.6	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

4.3

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

2.8

1.4

[email protected]

4.3

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

2.8

1.4

[email protected]

4.3

2.0

MEDIUM

AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:M): Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:N): No availability impact.

8.6

2.9

[email protected]

OS Trackers for CVE-2021-21366

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2021-21366 not yet assigned priority: Debian including 1 source packages (node-xmldom), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-21366
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2021-21366
`ubuntu`	medium	CVE-2021-21366 medium priority: Ubuntu including 1 source packages (node-xmldom), 11 status rows across 11 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, trusty, upstream, xenial): DNE 3, ignored 3, not-affected 3, released 2.	https://ubuntu.com/security/CVE-2021-21366

Affected software / configurations for CVE-2021-21366

Vendor	Product	Version	Raw CPE
xmldom_project	xmldom	< 0.5.0	cpe:2.3:a:xmldom_project:xmldom::::::node.js::*
debian	debian_linux	10.0	cpe:2.3:o:debian:debian_linux:10.0:::::::*

References for CVE-2021-21366

URL	Tags
https://github.com/xmldom/xmldom/commit/d4201b9dfbf760049f457f9f08a3888d48835135	Patch
https://github.com/xmldom/xmldom/releases/tag/0.5.0	Release Notes
https://github.com/xmldom/xmldom/security/advisories/GHSA-h6q6-9hqw-rwfv	Vendor Advisory
https://lists.debian.org/debian-lts-announce/2023/01/msg00000.html	Mailing List Third Party Advisory
https://www.npmjs.com/package/xmldom	Product

URL

CVE-2021-21366 | Misinterpretation of malicious XML input

Exploit prediction scoring system (EPSS) score for CVE-2021-21366

Common vulnerability scoring system (CVSS) metrics for CVE-2021-21366

Weakness enumeration for CVE-2021-21366

GitHub Security Advisory for CVE-2021-21366

OS Trackers for CVE-2021-21366

Affected software / configurations for CVE-2021-21366

References for CVE-2021-21366