CVE-2021-3518 — Nokogiri Implements libxml2 version vulnerable to use-after-free

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

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)
• 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.

1. Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Fedoraproject Fedora, Netapp Active Iq Unified Manager…).
2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
3. Apply the fixed version or the patch documented under Remediation.
4. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
5. EPSS ahead of 98% of scored CVEs: prioritize it in the patch queue.
6. 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.

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.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-416 · Use After Free

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 21.86%

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
  Oct 14, 2026 · GitHub Security Advisories
• Affected products added · rubygems/nokogiri
  Oct 14, 2026 · GitHub Security Advisories
• Record published
  Oct 14, 2026
• Fix documented
  Oct 14, 2026 · NIST National Vulnerability Database
• Affected products added · xmlsoft/libxml2, debian/debian linux, redhat/jboss core services, redhat/enterprise linux, fedoraproject/fedora, netapp/
  Oct 14, 2026 · NIST National Vulnerability Database
• CVSS changed · 8.8
  Oct 14, 2026 · NIST National Vulnerability Database
• Source status changed · → Modified
  Oct 14, 2026 · NIST National Vulnerability Database
• Record created in this database
  Oct 14, 2026 · Alertas do Telegram
• 2021
• CVE published
  May 18, 2021 · redhat

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

29 on the record

• www.oracle.com/security-alerts/cpuoct2021.html
  Patch, Third Party Advisory, x_refsource_MISC, NIST National Vulnerability Database
• bugzilla.redhat.com/show_bug.cgi
  Issue Tracking, Patch, Third Party Advisory, x_refsource_MISC, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpuapr2022.html
  Patch, Third Party Advisory, x_refsource_MISC, NIST National Vulnerability Database
• support.apple.com/kb/HT212602
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QVM4UJ
  GitHub Security Advisories
• lists.debian.org/debian-lts-announce/2021/05/msg00008.html
  Mailing List, Third Party Advisory, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• security.netapp.com/advisory/ntap-20210625-0002/
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• github.com/rubysec/ruby-advisory-db/blob/master/gems/nokogiri/CVE-2021-3518.yml
  GitHub Security Advisories
• github.com/advisories/GHSA-v4f8-2847-rwm7
  GitHub Security Advisories
• seclists.org/fulldisclosure/2021/Jul/58
  Mailing List, Third Party Advisory, mailing-list, x_refsource_FULLDISC, NIST National Vulnerability Database
• lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4
  mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• github.com/sparklemotion/nokogiri/blob/2edbbef95f1dc12c1ddc5ebda71b9159026245fe/
  GitHub Security Advisories
• nokogiri.org/CHANGELOG.html
  GitHub Security Advisories
• support.apple.com/kb/HT212605
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QVM4
  vendor-advisory, x_refsource_FEDORA, NIST National Vulnerability Database
• lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b
  mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• support.apple.com/kb/HT212604
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b
  GitHub Security Advisories
• seclists.org/fulldisclosure/2021/Jul/59
  Mailing List, Third Party Advisory, mailing-list, x_refsource_FULLDISC, NIST National Vulnerability Database
• seclists.org/fulldisclosure/2021/Jul/55
  Mailing List, Third Party Advisory, mailing-list, x_refsource_FULLDISC, NIST National Vulnerability Database
• lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/BZOMV5
  GitHub Security Advisories
• lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BZOM
  vendor-advisory, x_refsource_FEDORA, NIST National Vulnerability Database
• support.apple.com/kb/HT212601
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• security.gentoo.org/glsa/202107-05
  Third Party Advisory, vendor-advisory, x_refsource_GENTOO, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpujul2022.html
  Not Applicable, x_refsource_MISC, NIST National Vulnerability Database
• cert-portal.siemens.com/productcert/html/ssa-398330.html
  NIST National Vulnerability Database
• nvd.nist.gov/vuln/detail/CVE-2021-3518
  GitHub Security Advisories
• seclists.org/fulldisclosure/2021/Jul/54
  Mailing List, Third Party Advisory, mailing-list, x_refsource_FULLDISC, NIST National Vulnerability Database
• lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4
  GitHub Security Advisories

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
• Medium CVE-2026-104047 Sssd: sssd: information disclosure via query injection in entra id lookups 9d
• High CVE-2026-104048 Sssd: sssd: authorization bypass via cross-domain username collision in hbac evaluation 9d
• High CVE-2026-102558 Libsoup: libsoup: heap buffer overflow during websocket receive-buffer growth 16d
• Critical CVE-2026-102560 Libsoup: libsoup: heap buffer overflow during outgoing permessage-deflate buffer growth 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 CISA SSVC assessment.
• 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-2021-3518 is "Nokogiri Implements libxml2 version vulnerable to use-after-free", 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 8.8 describes technical severity. EPSS 21.86% 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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