PatchTheCVECVE-2021-37750: The Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.18.5 and 1.19.x before 1.19.3 has a NU
49
This month
MEDIUM 6.5WATCHLISTUPGRADEMITIGATEMITIGATE
CVE-2021-37750 is a medium-severity flaw (CVSS 6.5) affecting kerberos 5, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
The Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.18.5 and 1.19.x before 1.19.3 has a NULL pointer dereference in kdc/do_tgs_req.c via a FAST inner body that lacks a server field.
Why this priority
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 6.5 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | Low |
| User interaction | None |
| EPSS exploit chance | 2.5% (top 15%) |
| CISA exploited list | No |
| Weakness | CWE-476 |
| Published | 2021-08-23 |
| Last modified | 2026-10-14 |
Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
mit kerberos 5 UPGRADE
Affected: < 1.18.5 · >= 1.19.0 and < 1.19.3
Fixed in: 1.18.5, 1.19.3
Safe to downgrade to: a release before 1.19.0
1. Check installed version
apt-cache policy kerberos-5 || rpm -q kerberos-5 || kerberos-5 --version
2. UPGRADE to 1.18.5 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade kerberos-5
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade kerberos-5
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 1.19.0 (Debian / Ubuntu)
apt-cache madison kerberos-5
sudo apt install kerberos-5=<VERSION_BEFORE_1.19.0>
sudo apt-mark hold kerberos-5
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list kerberos-5
sudo dnf downgrade kerberos-5-<VERSION_BEFORE_1.19.0>
sudo dnf versionlock add kerberos-5
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.
fedoraproject fedora MITIGATE
Affected: 33
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.
starwindsoftware starwind virtual san DOWNGRADE
Affected: v8r13 14338
Fixed in: no fixed release known
Safe to downgrade to: a release before v8r13
1. Check installed version
apt-cache policy starwind-virtual-san || rpm -q starwind-virtual-san || starwind-virtual-san --version
2. No fixed release: DOWNGRADE to a release before v8r13 (Debian / Ubuntu)
apt-cache madison starwind-virtual-san
sudo apt install starwind-virtual-san=<VERSION_BEFORE_v8r13>
sudo apt-mark hold starwind-virtual-san
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list starwind-virtual-san
sudo dnf downgrade starwind-virtual-san-<VERSION_BEFORE_v8r13>
sudo dnf versionlock add starwind-virtual-san
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.
oracle communications cloud native core network slice selection function DOWNGRADE
Affected: 22.1.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 22.1.0
1. Check installed version
apt-cache policy communications-cloud-native-core-network-slice-selection-function || rpm -q communications-cloud-native-core-network-slice-selection-function || communications-cloud-native-core-network-slice-selection-function --version
2. No fixed release: DOWNGRADE to a release before 22.1.0 (Debian / Ubuntu)
apt-cache madison communications-cloud-native-core-network-slice-selection-function
sudo apt install communications-cloud-native-core-network-slice-selection-function=<VERSION_BEFORE_22.1.0>
sudo apt-mark hold communications-cloud-native-core-network-slice-selection-function
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list communications-cloud-native-core-network-slice-selection-function
sudo dnf downgrade communications-cloud-native-core-network-slice-selection-function-<VERSION_BEFORE_22.1.0>
sudo dnf versionlock add communications-cloud-native-core-network-slice-selection-function
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.
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.
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-2021-37750?
kerberos 5: upgrade to 1.18.5, 1.19.3; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2021-37750 being exploited?
CVE-2021-37750 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-2021-37750 affect?
CVE-2021-37750 affects kerberos 5, fedora, debian linux. Severity is medium (CVSS 6.5). The Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.18.5 and 1.19.x before 1.19.3 has a NULL pointer dereference in kdc/do_tgs_req.c via a FAST inner body that lacks a server field.
How urgent is CVE-2021-37750?
Priority 49/100. On your watchlist
Software pages
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