CVE-2021-3517 — nokogiri
HIGHCVE-2021-3517 is a high-severity (CVSS 8.6) Out-of-bounds Write vulnerability in nokogiri. EPSS puts its 30-day exploitation probability at 17.0% (97th percentile). A fix is available for nokogiri — see the affected versions and patch details below.
Nokogiri contains libxml Out-of-bounds Write vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-3517.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
nokogiriReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
There is a flaw in the xml entity encoding functionality of libxml2 in versions before 2.9.11. An attacker who is able to supply a crafted file to be processed by an application linked with the affected functionality of libxml2 could trigger an out-of-bounds read. The most likely impact of this flaw is to application availability, with some potential impact to confidentiality and integrity if an attacker is able to use memory information to further exploit the application.
Nokogiri prior to version 1.11.4 used a vulnerable version of libxml2. Nokogiri 1.11.4 updated libxml2 to version 2.9.11 to address this and other vulnerabilities in libxml2.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | nokogiri | all versions | 1.11.4bundle update nokogiri --conservative |
Affected Products
debian linuxdebianfedorafedoraprojectactive iq unified managernetappclustered data ontapnetappclustered data ontap antivirus connectornetappe-series santricity os controllernetappDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nokogiri, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nokogiri to 1.11.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3517 is resolved across your whole dependency graph.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This flaw is out of support scope for Red Hat Enterprise Linux 6 and 7. To learn more about Red Hat Enterprise Linux support life cycles, please see https://access.redhat.com/support/policy/updates/errata .
| Product | Fixed in | Advisory |
|---|---|---|
| JBoss Core Services for RHEL 8 | jbcs-httpd24-apr-util-0:1.6.1-91.el8jbcs | RHSA-2022:1389 |
| Red Hat Enterprise Linux 8 | libxml2-0:2.9.7-9.el8_4.2 | RHSA-2021:2569 |
| Red Hat JBoss Core Services | libxml2 | RHSA-2022:1390 |
| Red Hat Migration Toolkit for Containers 1.4 | rhmtc/openshift-migration-controller-rhel8:v1.4.6-4 | RHBA-2021:2854 |
Frequently Asked Questions
Is CVE-2021-3517 in your dependencies?
Find it across RubyGems, including transitive dependencies.