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CVE-2021-3517: There is a flaw in the xml entity encoding functionality of libxml2 in versions before 2.9.11

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This week
HIGH 8.6REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2021-3517 is a high-severity flaw (CVSS 8.6) affecting libxml2, jboss core services, enterprise linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 furth

Why this priority

  • High severity
  • EPSS top 3%: very likely to be exploited
  • Remotely exploitable, no login, no user action
  • On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score8.6 (High)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance17.0% (top 3%)
CISA exploited listNo
WeaknessCWE-787, CWE-125
Published2021-05-19
Last modified2026-10-14
Publisher (CNA): Red Hat, Inc. · Vendor: debian · fedoraproject · netapp · redhat · xmlsoft

Share: LinkedIn · X · Reddit

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

xmlsoft libxml2 UPGRADE
Affected: < 2.9.11
Fixed in: 2.9.11
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy libxml2 || rpm -q libxml2 || libxml2 --version
2. UPGRADE to 2.9.11 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade libxml2
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade libxml2
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
redhat jboss core services MITIGATE
Affected: all versions
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy jboss-core-services || rpm -q jboss-core-services || jboss-core-services --version
No fixed or unaffected release known
Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.
redhat enterprise linux MITIGATE
Affected: 8.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 8.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
fedoraproject fedora MITIGATE
Affected: 33 · 34
Fixed in: no fixed release known
Safe to downgrade to: a release before 33
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
debian debian linux MITIGATE
Affected: 9.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 9.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
netapp active iq unified manager MITIGATE
Affected: all versions
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy active-iq-unified-manager || rpm -q active-iq-unified-manager || active-iq-unified-manager --version
No fixed or unaffected release known
Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.
Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-3517?

libxml2: upgrade to 2.9.11; jboss core services: mitigate or apply the listed mitigation; enterprise linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-3517 being exploited?

CVE-2021-3517 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-3517 affect?

CVE-2021-3517 affects libxml2, jboss core services, enterprise linux. Severity is high (CVSS 8.6). 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 trigge

How urgent is CVE-2021-3517?

Priority 64/100. High severity; EPSS top 3%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · JBoss and WildFly vulnerabilities · libxml2 vulnerabilities

Related CVEs

References

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