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CVE-2020-28196: MIT Kerberos 5 (aka krb5) before 1.17.2 and 1.18.x before 1.18.3 allows unbounded recursion via an ASN.1-encod

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HIGH 7.5REMOTEUPGRADEMITIGATEMITIGATE

CVE-2020-28196 is a high-severity flaw (CVSS 7.5) affecting kerberos 5, fedora, active iq unified manager. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

MIT Kerberos 5 (aka krb5) before 1.17.2 and 1.18.x before 1.18.3 allows unbounded recursion via an ASN.1-encoded Kerberos message because the lib/krb5/asn.1/asn1_encode.c support for BER indefinite lengths lacks a recursion limit.

Why this priority

  • High severity
  • EPSS top 9%: very likely to be exploited
  • Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score7.5 (High)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance4.4% (top 9%)
CISA exploited listNo
WeaknessCWE-674
Published2020-11-06
Last modified2026-10-14
Publisher (CNA): MITRE · Vendor: fedoraproject · mit · netapp

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

Am I affected?

Timeline

mit kerberos 5 UPGRADE
Affected: < 1.17.2 · >= 1.18.0 and < 1.18.3
Fixed in: 1.17.2, 1.18.3
Safe to downgrade to: a release before 1.18.0
1. Check installed version
apt-cache policy kerberos-5 || rpm -q kerberos-5 || kerberos-5 --version
2. UPGRADE to 1.17.2 (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 1.18.0 (Debian / Ubuntu)
apt-cache madison kerberos-5 sudo apt install kerberos-5=<VERSION_BEFORE_1.18.0> 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_1.18.0> 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: 31
Fixed in: no fixed release known
Safe to downgrade to: a release before 31
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.
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.
netapp cloud backup 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 cloud-backup || rpm -q cloud-backup || cloud-backup --version
No fixed or unaffected release known
Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.
netapp oncommand insight 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 oncommand-insight || rpm -q oncommand-insight || oncommand-insight --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-2020-28196?

kerberos 5: upgrade to 1.17.2, 1.18.3; fedora: mitigate or apply the listed mitigation; active iq unified manager: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-28196 being exploited?

CVE-2020-28196 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-2020-28196 affect?

CVE-2020-28196 affects kerberos 5, fedora, active iq unified manager. Severity is high (CVSS 7.5). MIT Kerberos 5 (aka krb5) before 1.17.2 and 1.18.x before 1.18.3 allows unbounded recursion via an ASN.1-encoded Kerberos message because the lib/krb5/asn.1/asn1_encode.c support for BER indefinite lengths lacks a recursion limit.

How urgent is CVE-2020-28196?

Priority 54/100. High severity; EPSS top 9%: very likely to be exploited; Remotely exploitable, no login, no user action

Related CVEs

References

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