CVE-2020-25717

Q: What is the severity of CVE-2020-25717?

CVE-2020-25717 has a CVSS score of 8.1 (HIGH). CVE-2020-25717 is a privilege escalation vulnerability in Samba's domain user mapping mechanism. Authenticated attackers can exploit this flaw to gain elevated privileges on Samba servers. This affects Samba installations configured with domain user mappings.

8.1 HIGH

📋 TL;DR

CVE-2020-25717 is a privilege escalation vulnerability in Samba's domain user mapping mechanism. Authenticated attackers can exploit this flaw to gain elevated privileges on Samba servers. This affects Samba installations configured with domain user mappings.

💻 Affected Systems

Products:

Samba

Versions: All versions before 4.13.17, 4.14.12, and 4.15.5

Operating Systems: Linux, Unix-like systems running Samba

Default Config Vulnerable: ✅ No

Notes: Only affects Samba installations configured with 'username map' functionality where domain users are mapped to local users. Default installations without custom user mappings are not vulnerable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Full system compromise where an authenticated attacker gains root/administrator privileges on the Samba server, potentially leading to complete control over the system and access to all shared data.

🟠

Likely Case

Privilege escalation allowing attackers to access restricted files and directories they shouldn't have permission to, potentially leading to data theft or further lateral movement.

🟢

If Mitigated

Limited impact with proper network segmentation, minimal user privileges, and monitoring in place, though the vulnerability still exists.

🌐 Internet-Facing: MEDIUM - While authentication is required, internet-facing Samba servers with exposed shares could be targeted by attackers who obtain valid credentials.

🏢 Internal Only: HIGH - Internal attackers with legitimate credentials can exploit this to escalate privileges and potentially compromise the entire Samba server.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires authenticated access to the Samba server. The vulnerability is in the user mapping logic, making exploitation relatively straightforward once authenticated.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Samba 4.13.17, 4.14.12, 4.15.5 or later

Vendor Advisory: https://www.samba.org/samba/security/CVE-2020-25717.html

Restart Required: Yes

Instructions:

1. Identify current Samba version. 2. Update to patched version via package manager (apt-get upgrade samba, yum update samba, etc.). 3. Restart Samba services (systemctl restart smbd nmbd). 4. Verify the update was successful.

🔧 Temporary Workarounds

Disable username map functionality

linux

Remove or disable username map configurations if not required

# Edit smb.conf and remove or comment out 'username map' lines
# Then restart Samba: systemctl restart smbd nmbd

Restrict user access

linux

Limit which users can authenticate to Samba shares

# In smb.conf, use 'valid users' or 'invalid users' directives to restrict access

🧯 If You Can't Patch

Implement strict network segmentation to isolate Samba servers from critical systems
Enforce principle of least privilege for all Samba users and monitor for unusual access patterns

🔍 How to Verify

Check if Vulnerable:

Check Samba version with 'smbd --version' and verify if it's below patched versions. Also check smb.conf for 'username map' directives.

Check Version:

smbd --version

Verify Fix Applied:

Confirm Samba version is 4.13.17+, 4.14.12+, or 4.15.5+ using 'smbd --version'. Test user mapping functionality if required.

📡 Detection & Monitoring

Log Indicators:

Unusual privilege escalation attempts in Samba logs
Multiple failed authentication attempts followed by successful privileged access
Access to restricted files by users not mapped to those permissions

Network Indicators:

Unusual SMB traffic patterns from authenticated users
Multiple authentication requests from single source

SIEM Query:

source="samba_logs" AND ("privilege escalation" OR "access violation" OR "permission denied" followed by successful access)

📊 Metadata

CVE ID: CVE-2020-25717

CVSS v3 Score: 8.1 (HIGH)

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

CWE: CWE-20

Published: February 18, 2022

Last Updated: November 21, 2024

🔗 References

https://bugzilla.redhat.com/show_bug.cgi?id=2019672 Issue Tracking,Patch,Third Party Advisory
https://security.gentoo.org/glsa/202309-06
https://www.samba.org/samba/security/CVE-2020-25717.html Mitigation,Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2019672 Issue Tracking,Patch,Third Party Advisory
https://security.gentoo.org/glsa/202309-06
https://www.samba.org/samba/security/CVE-2020-25717.html Mitigation,Vendor Advisory

📋 TL;DR

💻 Affected Systems

📦 What is this software?

Codeready Linux Builder by Redhat

Debian Linux by Debian

Debian Linux by Debian

Enterprise Linux by Redhat

Enterprise Linux by Redhat

Enterprise Linux Desktop by Redhat

Enterprise Linux Eus by Redhat

Enterprise Linux Eus by Redhat

Enterprise Linux For Ibm Z Systems by Redhat

Enterprise Linux For Ibm Z Systems by Redhat

Enterprise Linux For Ibm Z Systems Eus by Redhat

Enterprise Linux For Ibm Z Systems Eus by Redhat

Enterprise Linux For Power Big Endian by Redhat

Enterprise Linux For Power Little Endian by Redhat

Enterprise Linux For Power Little Endian by Redhat

Enterprise Linux For Power Little Endian Eus by Redhat

Enterprise Linux For Power Little Endian Eus by Redhat

Enterprise Linux For Scientific Computing by Redhat

Enterprise Linux Resilient Storage by Redhat

Enterprise Linux Server by Redhat

Enterprise Linux Server Aus by Redhat

Enterprise Linux Server Aus by Redhat

Enterprise Linux Server Tus by Redhat

Enterprise Linux Server Update Services For Sap Solutions by Redhat

Enterprise Linux Server Update Services For Sap Solutions by Redhat

Enterprise Linux Tus by Redhat

Enterprise Linux Workstation by Redhat

Fedora by Fedoraproject

Fedora by Fedoraproject

Fedora by Fedoraproject

Gluster Storage by Redhat

Gluster Storage by Redhat

Openstack by Redhat

Openstack by Redhat

Openstack by Redhat

Samba by Samba

Samba by Samba

Samba by Samba

Ubuntu Linux by Canonical

Ubuntu Linux by Canonical

Ubuntu Linux by Canonical

Ubuntu Linux by Canonical

Virtualization by Redhat

Virtualization Host by Redhat

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable username map functionality

Restrict user access

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities