Authentication bypass in libssh (Alpine package)

1) Authentication bypass

EUVDB-ID: #VU15379

Risk: Low

CVSSv3.1: 9.1 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C]

CVE-ID: CVE-2018-10933

CWE-ID: CWE-592 - Authentication Bypass Issues

Exploit availability: Yes

Description

The vulnerability allows a remote attacker to bypass authentication on the target system.

The weakness exists due to coding error, when libssh receives the "SSH2_MSG_USERAUTH_SUCCESS" message. A remote attacker can send the SSH server "SSH2_MSG_USERAUTH_SUCCESS" message instead of the "SSH2_MSG_USERAUTH_REQUEST" message that a server usually expects and which libssh uses as a sign that an authentication procedure needs to initiate, bypass authentication procedures and gain access to a server with an SSH connection enabled without having to enter the password.

Mitigation

Install update from vendor's website.

Vulnerable software versions

libssh (Alpine package): 0.6.5-r0 - 0.7.5-r3

External links

http://git.alpinelinux.org/aports/commit/?id=4e617546654863ca795146a23e2e4c5037c7fa9f
http://git.alpinelinux.org/aports/commit/?id=3b5652246a72061f65136d4556b6eb8d87dad099
http://git.alpinelinux.org/aports/commit/?id=1729dd4c046d1b1dc146c28bf0d57b3e6557a228
http://git.alpinelinux.org/aports/commit/?id=5be0f2a6ade9a4196102468c29c4e05068caf178
http://git.alpinelinux.org/aports/commit/?id=5c43888ac21b20f04716252828c30995461222a3
http://git.alpinelinux.org/aports/commit/?id=7838ef4a7544c4d8c742eeaae9a6477f38a67313
http://git.alpinelinux.org/aports/commit/?id=91c2fc713213cbbf8dd105a185465c4a3427fa54

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, a fully functional exploit for this vulnerability is available.