CVE-2021-42521

VTK NULL pointer dereference vulnerability

7.5 HighFix available

There is a NULL pointer dereference vulnerability in VTK before 9.2.5, and it lies in IO/Infovis/vtkXMLTreeReader.cxx. The vendor didn't check the return value of libxml2 API 'xmlDocGetRootElement', and try to dereference it. It is unsafe as the return value can be NULL and that NULL pointer dereference may crash the application.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

1.32%Up 0.4 points since Aug 26, 2022

What each source reports

NVD Score used 7.5

Record: CVE-2021-42521
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-400, CWE-476
Updated: 2026-11-02

CVE List No score

Record: CVE-2021-42521
Weakness: CWE-400
Updated: 2026-11-02

EUVDEUVD-2022-0352 No score

Record: EUVD-2022-0352
Updated: 2026-11-03

GitHub AdvisoriesGHSA-xfhg-9pjg-xg7g 8.7

VTK NULL pointer dereference vulnerability

There is a NULL pointer dereference vulnerability in VTK, and it lies in IO/Infovis/vtkXMLTreeReader.cxx. The vendor didn't check the return value of libxml2 API 'xmlDocGetRootElement', and try to dereference it. It is unsafe as the return value can be NULL and that NULL pointer dereference may crash the application.

Record: GHSA-xfhg-9pjg-xg7g
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-400, CWE-476
Updated: 2026-11-02

OSV 7.5

Record: CVE-2021-42521
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVDEBIAN-CVE-2021-42521 7.5

Record: DEBIAN-CVE-2021-42521
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVGHSA-xfhg-9pjg-xg7g 8.7

VTK NULL pointer dereference vulnerability

Record: GHSA-xfhg-9pjg-xg7g
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-400, CWE-476
Updated: 2026-11-02

OSVUBUNTU-CVE-2021-42521 7.5

Record: UBUNTU-CVE-2021-42521
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVPYSEC-2022-255 No score

Record: PYSEC-2022-255
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`vtk` PyPI	before 9.0.1	9.0.1
`vtk9` Debian:12	All versions, plus listed versions 9.1.0+really9.1.0+dfsg2-59.1.0+really9.1.0+dfsg2-5+deb12u19.1.0+really9.1.0+dfsg2-69.1.0+really9.1.0+dfsg2-79.1.0+really9.1.0+dfsg2-7.1 Show 45 moreShow less 9.1.0+really9.1.0+dfsg2-89.2.6+dfsg1-1+exp19.2.6+dfsg1-1+exp29.3.0+dfsg1-19.3.0+dfsg1-1.19.3.0+dfsg1-1~exp19.3.0+dfsg1-1~exp29.3.0+dfsg1-1~exp39.3.0+dfsg1-1~exp49.3.0+dfsg1-29.3.0+dfsg1-39.3.0+dfsg1-3+hurd.19.3.0+dfsg1-49.3.0+dfsg1-4+m68k9.3.0+dfsg1-4.1+hurd.19.3.0+dfsg1-59.3.0+dfsg1-69.3.0+dfsg1-79.5.2+dfsg1-1~exp19.5.2+dfsg2-19.5.2+dfsg2-1~exp19.5.2+dfsg2-1~exp29.5.2+dfsg2-1~exp39.5.2+dfsg2-1~exp49.5.2+dfsg2-29.5.2+dfsg2-39.5.2+dfsg2-49.5.2+dfsg3-19.5.2+dfsg3-29.5.2+dfsg3-39.5.2+dfsg3-49.5.2+dfsg3-59.5.2+dfsg3-69.5.2+dfsg3-79.5.2+dfsg3-89.5.2+dfsg4-19.5.2+dfsg4-29.5.2+dfsg4-39.5.2+dfsg4-49.5.2+dfsg4-59.6.2+dfsg1-1exp19.6.2+dfsg1-1exp29.6.2+dfsg1-1exp39.6.2+dfsg1-1exp49.6.2+dfsg1-1exp5	None known
`vtk9` Debian:13	before 9.1.0+really9.1.0+dfsg2-8	9.1.0+really9.1.0+dfsg2-8
`vtk9` Debian:14	before 9.1.0+really9.1.0+dfsg2-8	9.1.0+really9.1.0+dfsg2-8
`vtk` PyPI	before 9.0.1, plus listed versions 8.1.08.1.18.1.29.0.0	9.0.1
`vtk` Ubuntu:Pro:14.04:LTS	All versions, plus listed versions 5.8.0-14ubuntu15.8.0-14ubuntu35.8.0-14.1ubuntu25.8.0-14.1ubuntu35.8.0-14.1ubuntu3+esm1	None known
`vtk6` Ubuntu:14.04:LTS	All versions, plus listed versions 6.0.0-16.0.0-26.0.0-36.0.0-46.0.0-6	None known
`vtk` Ubuntu:Pro:16.04:LTS	All versions, plus listed versions 5.10.1+dfsg-25.10.1+dfsg-2build35.10.1+dfsg-2.1build15.10.1+dfsg-2.1ubuntu0.1~esm1	None known
`vtk6` Ubuntu:Pro:16.04:LTS	All versions, plus listed versions 6.2.0+dfsg1-4ubuntu56.2.0+dfsg1-4ubuntu66.2.0+dfsg1-86.2.0+dfsg1-96.2.0+dfsg1-10build16.2.0+dfsg1-10ubuntu0.16.2.0+dfsg1-10ubuntu0.1+esm1	None known
`vtk6` Ubuntu:18.04:LTS	All versions, plus listed versions 6.3.0+dfsg1-10build16.3.0+dfsg1-10build26.3.0+dfsg1-10build36.3.0+dfsg1-116.3.0+dfsg1-11build1	None known

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Affected packages
Package	Affected	Fixed
`vtk7` Ubuntu:18.04:LTS	All versions, plus listed versions 7.1.1+dfsg1-2	None known
`vtk6` Ubuntu:20.04:LTS	All versions, plus listed versions 6.3.0+dfsg2-2build76.3.0+dfsg2-4build16.3.0+dfsg2-56.3.0+dfsg2-5build16.3.0+dfsg2-5build2	None known
`vtk7` Ubuntu:20.04:LTS	All versions, plus listed versions 7.1.1+dfsg1-12build27.1.1+dfsg2-17.1.1+dfsg2-1build17.1.1+dfsg2-1ubuntu37.1.1+dfsg2-2ubuntu1	None known
`vtk7` Ubuntu:22.04:LTS	All versions, plus listed versions 7.1.1+dfsg2-107.1.1+dfsg2-10ubuntu27.1.1+dfsg2-10ubuntu37.1.1+dfsg2-10.17.1.1+dfsg2-10.1build1	None known
`vtk9` Ubuntu:22.04:LTS	All versions, plus listed versions 9.0.1+dfsg1-89.1.0+really9.0.3+dfsg1-49.1.0+really9.0.3+dfsg1-4build19.1.0+really9.1.0+dfsg2-39.1.0+really9.1.0+dfsg2-3build1	None known
`vtk9` Ubuntu:24.04:LTS	All versions, plus listed versions 9.1.0+really9.1.0+dfsg2-79.1.0+really9.1.0+dfsg2-7build19.1.0+really9.1.0+dfsg2-7.1build29.1.0+really9.1.0+dfsg2-7.1build3	None known

History

History
Recorded	Changed	Sources
Nov 3, 2026	aliases	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-42521 is a high vulnerability (CVSS 7.5) in Vtk, published August 25, 2022. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.32%, the 70th percentile. Fixed in vtk 9.0.1.

References

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This page doesn't list everything

Left out here: 11 versions. The JSON record has them.