CVE-2021-42521

Exp

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.

Published: 2022-08-25 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-42521 is rated High Exploit Risk (66.2/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.07%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-42521

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-42521

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-25 1.03% 1.07% +0.04%
2 2026-06-15 0.48% 1.03% +0.54%
3 2026-05-12 — 0.48% —

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-42521

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 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:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
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:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2021-42521

GitHub Security Advisory for CVE-2021-42521

GHSA-xfhg-9pjg-xg7g · Severity: high · Ecosystem: pip — VTK NULL pointer dereference vulnerability

OS Trackers for CVE-2021-42521

vendor priority summary link
debian not yet assigned CVE-2021-42521 not yet assigned priority: Debian including 3 source packages (vtk6, vtk7, vtk9), 7 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 4, resolved 3. https://security-tracker.debian.org/tracker/CVE-2021-42521
ubuntu medium CVE-2021-42521 medium priority: Ubuntu including 4 source packages (vtk, vtk6, vtk7, vtk9), 52 status rows across 13 suites (bionic, focal, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 30, needed 14, ignored 6, not-affected 1, released 1. https://ubuntu.com/security/CVE-2021-42521

Affected software / configurations for CVE-2021-42521

Vendor Product Version Raw CPE
vtk vtk <= 9.0.0 cpe:2.3:a:vtk:vtk:*:*:*:*:*:*:*:*

References for CVE-2021-42521

cvelogic Threat Intelligence