Brute-force attack in Samba

Published: 2023-01-24
Risk Low
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2021-20251
Exploitation vector Local network
Public exploit N/A
Vulnerable software
Server applications / Directory software, identity management

Vendor Samba

Security Bulletin

This security bulletin contains one low risk vulnerability.

1) Race condition

EUVDB-ID: #VU71486

Risk: Low

CVSSv3.1: 3.7 [CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-20251

CWE-ID: CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Exploit availability: No


The vulnerability allows a remote attacker to perform a brute-force attack.

The vulnerability exists due to a race condition in Samba when incrementing bad password attempts. Each connection to Samba gets a separate process, and each process loads, increments, and saves the bad password count without any coordination. A remote attacker can perform a brute-force attack using multiple threats and bypass imposed limits on the number of allowed incorrect passwords.


Install updates from vendor's website.

Vulnerable software versions

Samba: 4.1.0 - 4.17.0

External links

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the local network (LAN).

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

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