CVE-2021-3517 — Nokogiri contains libxml Out-of-bounds Write vulnerability
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 17% (30-day exploitation probability)+15
- Technical severity (high)+6
- Automatable exploitation (SSVC)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — bugzilla.redhat.com (NIST National Vulnerability Database)
- Documented patch — www.oracle.com (NIST National Vulnerability Database)
- Documented patch — www.oracle.com (NIST National Vulnerability Database)
- Documented patch — www.oracle.com (NIST National Vulnerability Database)
- Rubygems Nokogiri: fixed in version 1.11.4 — github.com (GitHub Security Advisories)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Fedoraproject Fedora, Netapp Active Iq Unified Manager…).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- Apply the fixed version or the patch documented under Remediation.
- EPSS ahead of 97% of scored CVEs: prioritize it in the patch queue.
- Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Debian | Debian Linux | version 9.0 | Vulnerable | NIST National Vulnerability Database |
| Fedoraproject | Fedora | version 34version 33 | Vulnerable | NIST National Vulnerability Database |
| Netapp | Active Iq Unified Manager | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Clustered Data Ontap | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Clustered Data Ontap Antivirus Connector | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | E-series Santricity Os Controller | ≥ 11.0.0 and ≤ 11.70.1 | Vulnerable | NIST National Vulnerability Database |
| Netapp | E-series Santricity Storage Manager | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | E-series Santricity Web Services | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Hci H410c Firmware | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Hci Management Node | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Manageability Software Development Kit | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Oncommand Insight | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Oncommand Workflow Automation | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Ontap Select Deploy Administration Utility | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Santricity Unified Manager | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Snapdrive | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Snapmanager | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Netapp | Solidfire | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Oracle | Communications Cloud Native Core Network Function Cloud Native Environment | version 1.10.0 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Enterprise Manager Base Platform | version 13.4.0.0version 13.5.0.0 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Mysql Workbench | ≤ 8.0.26 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Openjdk | version 8-update301 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Peoplesoft Enterprise Peopletools | version 8.58 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Real User Experience Insight | version 13.4.1.0version 13.5.1.0 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Zfs Storage Appliance Kit | version 8.8 | Vulnerable | NIST National Vulnerability Database |
| Red Hat | Enterprise Linux | version 8.0 | Vulnerable | NIST National Vulnerability Database |
| Red Hat | Jboss Core Services | versions not specified by the source | Vulnerable | NIST National Vulnerability Database |
| Xmlsoft | Libxml2 | < 2.9.11 | Vulnerable | NIST National Vulnerability Database |
| Rubygems | Nokogiri | < 1.11.4 | Vulnerable | GitHub Security Advisories |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 8.6 | CVSS 3.1 | High | 3.9 | 4.7 | nvd@nist.gov via NIST National Vulnerability Database |
| 8.6 | CVSS 3.1 | High | 3.9 | 4.7 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database |
| 8.6 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
| 8.6 | CVSS 3.1 | High | — | — | CISA-ADP via CVE Program (cve.org) e CISA ADP |
| 7.5 | CVSS 2.0 | High | 10.0 | 6.4 | nvd@nist.gov via NIST National Vulnerability Database |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H (score shown at the top: nvd@nist.gov) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 16.99%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Timeline
What happened to this CVE, newest first.
- 2026
- Fix documented
- Affected products added · rubygems/nokogiri
- SSVC assessment updated
- Record published
- Fix documented
- Affected products added · xmlsoft/libxml2, redhat/jboss core services, redhat/enterprise linux, fedoraproject/fedora, debian/debian linux, netapp/
- CVSS changed · 8.6
- Source status changed · → Modified
- Record created in this database
- 2021
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
23 on the record
- www.oracle.com/security-alerts/cpuoct2021.html
- bugzilla.redhat.com/show_bug.cgi
- www.oracle.com/security-alerts/cpujan2022.html
- www.oracle.com/security-alerts/cpuapr2022.html
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/BZOMV5
- security.netapp.com/advisory/ntap-20211022-0004/
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QVM4UJ
- lists.debian.org/debian-lts-announce/2021/05/msg00008.html
- security.netapp.com/advisory/ntap-20210625-0002/
- lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QVM4
- github.com/advisories/GHSA-jw9f-hh49-cvp9
- github.com/rubysec/ruby-advisory-db/blob/master/gems/nokogiri/CVE-2021-3517.yml
- lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BZOM
- github.com/sparklemotion/nokogiri/issues/2233
- security.gentoo.org/glsa/202107-05
- www.oracle.com/security-alerts/cpujul2022.html
- cert-portal.siemens.com/productcert/html/ssa-398330.html
- gitlab.gnome.org/GNOME/libxml2/-/commit/8598060bacada41a0eb09d95c97744ff4e428f8e
- nvd.nist.gov/vuln/detail/CVE-2021-3517
- github.com/sparklemotion/nokogiri/blob/7c19ef5cc6b7c5c36827dd5495f857c6877ec8cf/
- github.com/sparklemotion/nokogiri/issues/2274
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-104046 Sssd: sssd: denial of service via incomplete identity provider authentication requests 9d
- Medium CVE-2026-104045 Sssd: sssd: denial of service via race condition in autofs responder 9d
- High CVE-2026-104048 Sssd: sssd: authorization bypass via cross-domain username collision in hbac evaluation 9d
- Medium CVE-2026-104047 Sssd: sssd: information disclosure via query injection in entra id lookups 9d
- High CVE-2026-102558 Libsoup: libsoup: heap buffer overflow during websocket receive-buffer growth 16d
- High CVE-2026-102555 Libsoup: libsoup: heap buffer overflow via uninitialized length in data-uri base64 decoding 16d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2021-3517 is "Nokogiri contains libxml Out-of-bounds Write vulnerability", rated High. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.6 describes technical severity. EPSS 16.99% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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