Brute-force attack in Samba

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

Description

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.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Samba: 4.1.0 - 4.17.0

External links

http://bugzilla.samba.org/show_bug.cgi?id=14611
http://gitlab.com/samba-team/samba/-/merge_requests/2708

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.