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CVE-2018-20217

20
FAUCET Score

CVE-2018-20217 is a Reachable Assertion vulnerability affecting the KDC in MIT Kerberos 5 versions prior to 1.17, as well as Debian Linux and Debian Kerberos. An attacker who obtains a krbtgt ticket using older encryption types (single-DES, triple-DES, or RC4) can crash the KDC by making an S4U2Self request. This vulnerability has a CVSS score of 5.3 (Medium), indicating a network-based attack with high attack complexity and potential for high availability impact. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 5-1.17CPE matchmatch criteria
cpe:2.3:a:mit:kerberos:*:*:*:*:*:*:*:*
8.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:8.0:*:*:*:*:*:*:*
9.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
1.6
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.42%
Probability of exploitation in next 30 days
EPSS Percentile
70.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0142 is in the 69th percentile among its peer group of 1,428 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (6)

github_advisorypatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Ansible Tower 3.4 for RHEL 7Fixed in: ansible-tower-34/ansible-tower-memcached:1.4.15-28
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Ansible Tower 3.4 for RHEL 7Fixed in: ansible-tower-35/ansible-tower-memcached:1.4.15-28
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Ansible Tower 3.4 for RHEL 7Fixed in: ansible-tower-37/ansible-tower-memcached-rhel7:1.4.15-28
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: krb5-0:1.15.1-37.el7_7.2
View patch
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: krb5

Vendor Advisories (1)

redhatCVE-2018-20217Moderate

krb5: Reachable assertion in the KDC using S4U2Self requests

Dec 2, 2018

References

krbdev.mit.edu / rt/Ticket/Display.html
PatchThird Party Advisory
github.com / krb5/krb5/commit/5e6d1796106df8ba6bc1973ee0917c170d929086
PatchThird Party Advisory
lists.debian.org / debian-lts-announce/2019/01/msg00020.html
Mailing ListThird Party Advisory
lists.debian.org / debian-lts-announce/2021/09/msg00019.html
Mailing ListThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/2KNHELH4YHNT6H2ESJWX2UIDXLBNGB2O
security.netapp.com / advisory/ntap-20190416-0006
Third Party Advisory