dbcve.org
FedoraOperating system · Fedoraproject

CVE-2019-14870

MEDIUM · 5.4 CVSS v3.1 Published 2019-12-10
Fix available
A fix is available. Upgrade to 4.9.17 / 4.10.11 or later.
See remediation →
60/100
Remediation priority · Elevated
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
All Samba versions 4.x.x before 4.9.17, 4.10.x before 4.10.11 and 4.11.x before 4.11.3 have an issue, where the S4U (MS-SFU) Kerberos delegation model includes a feature allowing for a subset of clients to be opted out of constrained delegation in any way, either S4U2Self or regular Kerberos authentication, by forcing all tickets for these clients to be non-forwardable. In AD this is implemented by a user attribute delegation_not_allowed (aka not-delegated), which translates to disallow-forwardable. However the Samba AD DC does not do that for S4U2Self and does set the forwardable flag even if the impersonated client has the not-delegated flag set.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Samba AD DC fails to honor the 'delegation_not_allowed' (not-delegated) user attribute when processing S4U2Self requests. While the attribute should cause tickets to be marked as non-forwardable to prevent credential delegation for protected accounts, the Samba implementation incorrectly sets the forwardable flag, allowing services to potentially impersonate users who should be protected from delegation.

MitigationUpgrade Samba to version 4.9.17, 4.10.11, or 4.11.3 or later. As a compensating control, restrict service accounts with constrained delegation permissions and monitor for unauthorized S4U ticket requests.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FedoraOperating system
Affected:= 30= 31
Ubuntu LinuxOperating system
Affected:= 14.04= 16.04= 18.04= 19.04= 19.10
Debian LinuxOperating system
Affected:= 9.0= 10.0
SambaApplication
Affected:>= 4.0.0, < 4.9.17>= 4.10.0, < 4.10.11>= 4.11.0, < 4.11.3
LeapOperating system
Affected:= 15.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Samba version
    Run 'samba --version' or check the installed package version with your system package manager (e.g., 'rpm -q samba' on Fedora/RHEL, 'dpkg -l samba' on Debian/Ubuntu)
    Affected if The installed version falls within the vulnerable ranges: >= 4.0.0 and < 4.9.17, OR >= 4.10.0 and < 4.10.11, OR >= 4.11.0 and < 4.11.3
  2. Confirm Samba is running as AD DC
    Check the smb.conf file (typically at /etc/samba/smb.conf) for 'server role = active directory domain controller' or inspect the output of 'samba-tool domain info'
    Affected if The system is configured as an Active Directory Domain Controller (AD DC)
  3. Identify users with delegation_not_allowed attribute
    Query Active Directory for users with the 'userAccountControl' attribute containing the ADS_UF_NOT_DELEGATED flag (value 0x00100000). Use 'samba-tool user list' combined with 'samba-tool user getpassword' or an ldapsearch query against the AD LDAP server on port 389
    Affected if There are user accounts in the AD domain that have the 'not-delegated' (delegation_not_allowed) flag set in their userAccountControl attribute
  4. Verify S4U2Self ticket generation behavior
    Attempt a S4U2Self request (using a tool like Krb5 or scripting with libraries such as python-krb5) for a user with the delegation_not_allowed flag set. Inspect the resulting service ticket to check the forwardable flag in the ticket flags field
    Affected if The generated ticket has the forwardable flag set (bit 1) despite the user being marked as not-delegated, indicating the vulnerability is present and exploitable

The environment is affected if Samba is running as an AD DC with a vulnerable version AND there exist users in the AD domain who have the delegation_not_allowed (not-delegated) flag set in their account attributes, as the flaw allows these protected accounts to have forwardable tickets issued incorrectly.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 4.9.17 / 4.10.11 / 4.11.3 or later
Fixed in 4.9.174.10.114.11.3
Interim mitigation

Upgrade Samba to version 4.9.17, 4.10.11, or 4.11.3 or later. As a compensating control, restrict service accounts with constrained delegation permissions and monitor for unauthorized S4U ticket requests.

Fix this in Fedora Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing8.0 h
  • Review / QA4.0 h
24.0 hours of engineering $4,160
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2019-14870 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data