LibSSH Flaw Allows Hackers to Take Over Servers Without Password

Oct 17, 2018

A four-year-old severe vulnerability has been discovered in
the Secure Shell (SSH) implementation library known as
Libssh that could allow anyone to completely bypass
authentication and gain unfettered administrative control over a
vulnerable server without requiring a password.

The security vulnerability, tracked as CVE-2018-10933, is
an authentication-bypass issue that was introduced in Libssh
version 0.6 released earlier 2014, leaving thousands of enterprise
servers open to hackers for the last four years.

But before you get frightened, you should know that neither the
widely used OpenSSH nor Github’s implementation of libssh was
affected by the vulnerability.

The vulnerability resides due to a coding error in Libssh and is
“ridiculously simple” to exploit.

According to a security advisory published ^[1]
Tuesday, all an attacker needs to do is sending an
“SSH2_MSG_USERAUTH_SUCCESS” message to a server with an SSH
connection enabled when it expects an “SSH2_MSG_USERAUTH_REQUEST”
message.

Due to a logical flaw in libssh, the library fails to validate
if the incoming “successful login” packet was sent by the server or
the client, and also fails to check if the authentication process
has been completed or not.

Therefore, if a remote attacker (client) sends this
“SSH2_MSG_USERAUTH_SUCCESS” response to libssh, it considers that
the authentication has been successful and will grant the attacker
access to the server, without needing to enter a password.

Although GitHub uses libssh, it confirms that its official
website and GitHub Enterprise are not affected by the vulnerability
due to how GitHub uses the library.

“We use a custom version of libssh; SSH2_MSG_USERAUTH_SUCCESS with
the libssh server is not relied upon for pubkey-based auth, which
is what we use the library for,” a GitHub security official said ^[2] on Twitter.

“Patches have been applied out of an abundance of caution, but GHE
[GitHub Enterprise] was never vulnerable to CVE-2018-10933.”

Shodan search shows that around 6,500 internet-facing servers
may be impacted due to the use of Libssh one or the other way.
The security bug was discovered by Peter Winter-Smith from NCC
Group, who responsibly disclosed the issue to Libssh.

The Libssh team addressed the issue with the release of its
updated libssh versions 0.8.4 and 0.7.6 on Tuesday, and the details
of the vulnerability were also released at the same time.

If you have Libssh installed on your website, and mainly if you
are using the server component, you are highly recommended to
install the updated versions of Libssh as soon as possible.

References

^{^}
published
(www.libssh.org)
^{^}
said
(twitter.com)

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OWASP TOP !0

Injection. Injection flaws, such as SQL, NoSQL, OS, and LDAP injection, occur when untrusted data is sent to an interpreter as part of a command or query. The attacker’s hostile data can trick the interpreter into executing unintended commands or accessing data without proper authorization. Broken Authentication. Application functions related to authentication and session management are often implemented incorrectly, allowing attackers to compromise passwords, keys, or session tokens, or to exploit other implementation flaws to assume other users’ identities temporarily or permanently. Sensitive Data Exposure. Many web applications and APIs do not properly protect sensitive data, such as financial, healthcare, and PII. Attackers may steal or modify such weakly protected data to conduct credit card fraud, identity theft, or other crimes. Sensitive data may be compromised without extra protection, such as encryption at rest or in transit, and requires special precautions when exchanged with the browser. XML External Entities (XXE). Many older or poorly configured XML processors evaluate external entity references within XML documents. External entities can be used to disclose internal files using the file URI handler, internal file shares, internal port scanning, remote code execution, and denial of service attacks. Broken Access Control. Restrictions on what authenticated users are allowed to do are often not properly enforced. Attackers can exploit these flaws to access unauthorized functionality and/or data, such as access other users’ accounts, view sensitive files, modify other users’ data, change access rights, etc. Security Misconfiguration. Security misconfiguration is the most commonly seen issue. This is commonly a result of insecure default configurations, incomplete or ad hoc configurations, open cloud storage, misconfigured HTTP headers, and verbose error messages containing sensitive information. Not only must all operating systems, frameworks, libraries, and applications be securely configured, but they must be patched/upgraded in a timely fashion. Cross-Site Scripting XSS. XSS flaws occur whenever an application includes untrusted data in a new web page without proper validation or escaping, or updates an existing web page with user-supplied data using a browser API that can create HTML or JavaScript. XSS allows attackers to execute scripts in the victim’s browser which can hijack user sessions, deface web sites, or redirect the user to malicious sites. Insecure Deserialization. Insecure deserialization often leads to remote code execution. Even if deserialization flaws do not result in remote code execution, they can be used to perform attacks, including replay attacks, injection attacks, and privilege escalation attacks. Using Components with Known Vulnerabilities. Components, such as libraries, frameworks, and other software modules, run with the same privileges as the application. If a vulnerable component is exploited, such an attack can facilitate serious data loss or server takeover. Applications and APIs using components with known vulnerabilities may undermine application defenses and enable various attacks and impacts. Insufficient Logging & Monitoring. Insufficient logging and monitoring, coupled with missing or ineffective integration with incident response, allows attackers to further attack systems, maintain persistence, pivot to more systems, and tamper, extract, or destroy data. Most breach studies show time to detect a breach is over 200 days, typically detected by external parties rather than internal processes or monitoring.

LibSSH Flaw Allows Hackers to Take Over Servers Without Password

References

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