CVE-2021-3537 — Nokogiri Implements libxml2 version vulnerable to null pointer dereferencing

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. 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-476 · NULL Pointer Dereference

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 3.60%

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, redhat/jboss core services, redhat/enterprise linux, debian/debian linux, fedoraproject/fedora, netapp/
  Oct 14, 2026 · NIST National Vulnerability Database
• CVSS changed · 5.9
  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 14, 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

17 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
• lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QVM4UJ
  GitHub Security Advisories
• github.com/advisories/GHSA-286v-pcf5-25rc
  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/sparklemotion/nokogiri/blob/2edbbef95f1dc12c1ddc5ebda71b9159026245fe/
  GitHub Security Advisories
• nokogiri.org/CHANGELOG.html
  GitHub Security Advisories
• nvd.nist.gov/vuln/detail/CVE-2021-3537
  GitHub Security Advisories
• lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QVM4
  vendor-advisory, x_refsource_FEDORA, 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
• github.com/rubysec/ruby-advisory-db/blob/master/gems/nokogiri/CVE-2021-3537.yml
  GitHub Security Advisories
• 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

Elsewhere on this site

Related CVEs (same products)

• Medium CVE-2026-104046 Sssd: sssd: denial of service via incomplete identity provider authentication requests 8d
• Medium CVE-2026-104045 Sssd: sssd: denial of service via race condition in autofs responder 8d
• 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
• 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 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-2021-3537 is "Nokogiri Implements libxml2 version vulnerable to null pointer dereferencing", rated Medium. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.9 describes technical severity. EPSS 3.60% 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.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.

Sign in or create an account to comment and suggest corrections.