#VU17350 Reachable Assertion in Kerberos 5 - CVE-2018-20217

Vulnerability identifier: #VU17350

Vulnerability risk: Low

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2018-20217

CWE-ID: CWE-617

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Kerberos 5
Client/Desktop applications / Software for system administration

Vendor: MIT

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a reachable assertion in in the KDC. A remote attacker can obtain a krbtgt ticket using an older encryption type (single-DES, triple-DES, or RC4) and crash the KDC by making an S4U2Self request.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Kerberos 5: 1.14 - 1.16.3

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External links
https://krbdev.mit.edu/rt/Ticket/Display.html?id=8763
https://github.com/krb5/krb5/commit/5e6d1796106df8ba6bc1973ee0917c170d929086

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.