Just Opening A Document in LibreOffice Can Hack Your Computer (Unpatched)

Jul 26, 2019

Are you using LibreOffice?

You should be extra careful about what document files you open
using the LibreOffice software over the next few days.

That’s because LibreOffice contains a severe unpatched code
execution vulnerability that could sneak malware into your system
as soon as you open a maliciously-crafted document file.

LibreOffice is one of the most popular and open source
alternatives to Microsoft Office suite and is available for
Windows, Linux and macOS systems.

Earlier this month, LibreOffice released the latest
version 6.2.5 of its software that addresses two severe
vulnerabilities (CVE-2019-9848 and CVE-2019-9849), but the patch
for the former has now been bypassed, security researcher Alex
Inführ claims.

Though Inführ has not yet disclosed details of the technique
that allowed him to bypass the patch, the impact of this
vulnerability remains the same, as explained below.

1.) CVE-2019-9848: This vulnerability, which still exists
in the latest version, resides in LibreLogo, a programmable turtle
vector graphics script that ships by default with LibreOffice.

LibreLogo allows users to specify pre-installed scripts in a
document that can be executed on various events such as
mouse-over.

Discovered by Nils Emmerich, the flaw could allow an attacker
to craft a malicious document that can silently execute arbitrary
python commands without displaying any warning to a targeted user.

“The big problem here is that the code is not translated well and
just supplying python code as the script code often results in the
same code after translation,” Emmerich said.

“Using forms and OnFocus event, it is even possible to get code
execution when the document is opened, without the need for a
mouse-over event.”

Emmerich also released a proof-of-concept
for this attack on his blog post.

2.) CVE-2019-9849: This vulnerability,
which you can fix by installing the latest available update, could
allow the inclusion of remote arbitrary content within a document
even when ‘stealth mode’ is enabled.
^[4]

The stealth mode is not enabled by default, but users can activate
it to instruct documents retrieve remote resources only from
trusted locations.

How to Protect Your System

Inführ has already notified LibreOffice team of the bypass
issue, but until the team releases a patch to fix the bypass, users
are recommended to update or reinstall the software without macros
or at least without LibreLogo component, by following the
below-mentioned steps.

Open the setup to start the installation
Select “Custom” installation
Expand “Optional Components”
Click on “LibreLogo” and select “This Feature Will Not Be
Available”
Click Next and then Install the software

^[1]^[2]^[3]

References

^{^}
released
(www.libreoffice.org)
^{^}
claims
(twitter.com)
^{^}
proof-of-concept for this attack
(insinuator.net)
^{^}
vulnerability
(www.libreoffice.org)

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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.

Just Opening A Document in LibreOffice Can Hack Your Computer (Unpatched)

How to Protect Your System

References

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