CVE-2018-20217 — A Reachable Assertion issue was discovered in the KDC in MIT Kerberos 5 (aka krb

A Reachable Assertion issue was discovered in the KDC in MIT Kerberos 5 (aka krb5) before 1.17. If an attacker can obtain a krbtgt ticket using an older encryption type (single-DES, triple-DES, or RC4), the attacker can crash the KDC by making an S4U2Self request.

01What is this vulnerability?

A Reachable Assertion issue was discovered in the KDC in MIT Kerberos 5 (aka krb5) before 1.17. If an attacker can obtain a krbtgt ticket using an older encryption type (single-DES, triple-DES, or RC4), the attacker can crash the KDC by making an S4U2Self request.

02Affected products

Vendor	Product	Versions
n	a / n/a	n/a

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2018-12-26T20:00:00.000Z
• Last modified: 2024-08-05T11:58:19.090Z

09References

• lists.fedoraproject.org — https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedorapro…
• krbdev.mit.edu — http://krbdev.mit.edu/rt/Ticket/Display.html?id=8763
• github.com — https://github.com/krb5/krb5/commit/5e6d1796106df8ba6bc1973ee0917c170d929086
• lists.debian.org — https://lists.debian.org/debian-lts-announce/2019/01/msg00020.html
• security.netapp.com — https://security.netapp.com/advisory/ntap-20190416-0006/
• lists.debian.org — https://lists.debian.org/debian-lts-announce/2021/09/msg00019.html