CVE-2020-17049

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Moderate Moderate Impact What does this mean?
7.2 CVSS v3 Base Score

Description

It was found that the Kerberos Key Distribution Center (KDC) delegation feature, Service for User (S4U), did not sufficiently protect the tickets it's providing from tempering. A malicious, authenticated service principal allowed to delegate could use this flaw to impersonate a non-forwardable user.

Statement

As a prerequisite to be vulnerable, a Key Distribution Center (KDC) must be able to accept delegation via the Service for User (S4U) extensions.

Version of MIT Kerberos KDC in Red Hat Enterprise Linux (provided by the krb5-server package) only allows use of the S4U extensions when configured with an LDAP backend. Furthermore, delegations are denied by default and delegation rules must be explicitly created by an administrator, between a given service principal and its targets. Such a rule would entitle that service to use delegation to the targets. This means that, in order to exploit the flaw, an attacker would require either to trick an administrator into adding a rule for a malicious service principal, or have the knowledge of an entitled principal's secret key. The victim principals would be limited to the ones allowed by the rules for that service.

This CVE only affects systems supporting constrained delegation as defined by MS-SFU. Vanilla MIT krb5 realms do not support this protocol extension.

In Red Hat Enterprise Linux version 8 and older and Red Hat Gluster Storage, Samba as an Active Directory Domain Controller is not supported, and thus is not affected by this flaw.

RHEL Identity Management (RHEL IdM) implements constrained delegation feature using Active Directory's Kerberos extensions called Service for User (S4U). The constrained delegation implementation may potentially be vulnerable if an attacker is capable to create constrained delegation rules. In RHEL IdM only administrators allowed to add constrained delegation rules and only one such rule exists by default for HTTP/.. principal on IdM server. Security of IdM server is the key to safety of the whole RHEL IdM deployment. If an attacker is able to impersonate the HTTP/.. service principal on IdM server, they would be able to overtake the whole deployment even without a Kerberos protocol vulnerability described by CVE-2020-17049. However, if an attacker cannot control any service with pre-existing constrained delegation rules and cannot force creation of the constrained delegation rules for other Kerberos services, they cannot utilize CVE-2020-17049 vulnerability against RHEL IdM.

Mitigation

In Red Hat Identity Management (IdM), the list of existing rules for service principals delegation can be obtained with the following commands :
$ ipa servicedelegationrule-find
$ ipa servicedelegationtarget-find
The services allowed to delegate must all be trusted.
By default, only HTTP/<IPA host>@<REALM>, corresponding to IdM's Web UI, is allowed to delegate.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2020-17049

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2020-17049

Content from msrc.microsoft.com is not included.https://msrc.microsoft.com/update-guide/vulnerability/CVE-2020-17049

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 7 samba Not affected
Red Hat Enterprise Linux 7 krb5 Will not fix
Red Hat Enterprise Linux 8 idm:DL1 Fixed RHSA-2024:0143
Red Hat Enterprise Linux 8 samba Not affected
Red Hat Enterprise Linux 8.6 Extended Update Support idm:DL1 Fixed RHSA-2024:0139
Red Hat Enterprise Linux 8.8 Extended Update Support idm:DL1 Fixed RHSA-2024:0137
Red Hat Enterprise Linux 9 krb5 Fixed RHSA-2023:2570
Red Hat Enterprise Linux 9 samba Not affected
Red Hat JBoss Core Services krb5 Not affected
Red Hat JBoss Enterprise Application Platform 6 krb5 Not affected
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Common Vulnerability Scoring System (CVSS) Score Details

Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 7.2 7.2
Attack Vector Network Network
Attack Complexity Low Low
Privileges Required High High
User Interaction None None
Scope Unchanged Unchanged
Confidentiality Impact High High
Integrity Impact High High
Availability Impact High High

CVSS v3 Vector

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

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

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

 For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

What can I do if my product is listed as "Will not fix"?

 A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

 A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

 In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our This content is not included.Red Hat Vulnerability Scanner Certification program.