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CVE-2019-5544: VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow Vulnerability

100
Patch now
CRITICAL 9.8EXPLOITEDREMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2019-5544 is a critical-severity flaw (CVSS 9.8) affecting horizon daas, esxi, enterprise linux desktop, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

OpenSLP as used in ESXi and the Horizon DaaS appliances has a heap overwrite issue. VMware has evaluated the severity of this issue to be in the Critical severity range with a maximum CVSSv3 base score of 9.8.

Why this priority

  • Critical severity
  • EPSS top 1%: very likely to be exploited
  • Exploited in the wild (CISA KEV)
  • Used in ransomware campaigns
  • Public exploit reference
  • CISA SSVC: automatable with total technical impact
  • Remotely exploitable, no login, no user action
  • On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score9.8 (Critical)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance98.1% (top 1%)
CISA exploited listYes, fix due 2022-05-03, used in ransomware
WeaknessCWE-787
Published2019-12-06
Last modified2026-06-17
Publisher (CNA): VMware · Vendor: redhat · vmware

Share: LinkedIn · X · Reddit

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

vmware horizon daas UPGRADE
Affected: >= 8.0.0 and < 9.0.0.0
Fixed in: 9.0.0.0
Safe to downgrade to: a release before 8.0.0
1. Check installed version
apt-cache policy horizon-daas || rpm -q horizon-daas || horizon-daas --version
2. UPGRADE to 9.0.0.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade horizon-daas
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade horizon-daas
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 8.0.0 (Debian / Ubuntu)
apt-cache madison horizon-daas sudo apt install horizon-daas=<VERSION_BEFORE_8.0.0> sudo apt-mark hold horizon-daas
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list horizon-daas sudo dnf downgrade horizon-daas-<VERSION_BEFORE_8.0.0> sudo dnf versionlock add horizon-daas
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
vmware esxi MITIGATE
Affected: 6.0 · 6.0 1 · 6.0 1a · 6.0 1b · 6.0 2 · 6.0 3 · 6.0 3a · 6.0 600-201504401
Fixed in: no fixed release known
Safe to downgrade to: a release before 6.0
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.
redhat enterprise linux desktop MITIGATE
Affected: 6.0 · 7.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 6.0
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.
redhat enterprise linux for ibm z systems MITIGATE
Affected: 6.0_s390x · 7.0_s390x
Fixed in: no fixed release known
Safe to downgrade to: a release before 6.0_s390x
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.
redhat enterprise linux for ibm z systems eus MITIGATE
Affected: 7.7_s390x
Fixed in: no fixed release known
Safe to downgrade to: a release before 7.7_s390x
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.
redhat enterprise linux for power big endian MITIGATE
Affected: 6.0_ppc64 · 7.0_ppc64
Fixed in: no fixed release known
Safe to downgrade to: a release before 6.0_ppc64
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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.
Fedora 46 · keepalived · FIXED · 2.4.3-1.fc46 · FEDORA-2026-0c83a077d7 · source
sudo dnf upgrade --advisory=FEDORA-2026-0c83a077d7
Fedora ELN · dracut · FIXED · 111-5.eln159 · FEDORA-2026-982407d9e3 · source
sudo dnf upgrade --advisory=FEDORA-2026-982407d9e3
RHEL 6 · openslp · FIXED · openslp-2.0.0-4.el6_10
sudo dnf upgrade --advisory=RHSA-2020:0199 rpm -q openslp
RHEL 7 · openslp · FIXED · openslp-2.0.0-8.el7_7
sudo dnf upgrade --advisory=RHSA-2019:4240 rpm -q openslp
RHEL 8 · openslp · NOT AFFECTED
RHEL 9 · openslp · NOT AFFECTED
Amazon Linux 2 · see advisory · FIXED · ALAS2-2019-1378 · source
sudo yum update --advisory=ALAS2-2019-1378

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Verify at the official source NVD · CVE Program · CISA KEV catalog · 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-2019-5544?

horizon daas: upgrade to 9.0.0.0; esxi: mitigate or apply the listed mitigation; enterprise linux desktop: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-5544 being exploited?

Yes. CVE-2019-5544 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2019-5544 affect?

CVE-2019-5544 affects horizon daas, esxi, enterprise linux desktop. Severity is critical (CVSS 9.8). OpenSLP as used in ESXi and the Horizon DaaS appliances has a heap overwrite issue. VMware has evaluated the severity of this issue to be in the Critical severity range with a maximum CVSSv3 base score of 9.8.

How urgent is CVE-2019-5544?

Priority 100/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Used in ransomware campaigns; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Software pages

VMware vulnerabilities

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