PoC Released for Outlook Flaw that Microsoft Patched 6 Month After Discovery

Jun 22, 2019

As we reported two days ago, Microsoft this week released an
updated version of its Outlook app for Android that patches a
severe remote code
execution vulnerability ^[1]
(CVE-2019-1105) that impacted over 100 million users.

However, at that time, very few details of the flaw were
available in the advisory, which just revealed that the earlier
versions of the email app contained a cross-site scripting (XSS)
flaw that could allow attackers to run scripts in the context of
the current user just by sending a specially crafted email to the
victims.

Now, Bryan Appleby from
F5 Networks, one of the security researchers who reported this
issue independently to Microsoft, released more details and
proof-of-concept for the Outlook vulnerability that he reported to
the tech giant almost six months ago.
^[2]

In a blog
post ^[3] published Friday,
Appleby revealed that while exchanging some JavaScript code with
his friends over an email, he accidentally discovered a cross-site
scripting (XSS) issue that could allow an attacker to embed an
iframe into the email.

In other words, the vulnerability resided in the way email
server parses HTML entities in the email messages.

Though JavaScript running inside an iframe can only access the
content within it, Appleby found that executing JavaScript code
inside the injected iframe can allow the attacker to read
app-related content in the context of logged-in Outlook user,
including their cookies, tokens and even some contents of their
email inbox.

The vulnerability, Appleby said, allowed him to “steal data from
the app—I could use it to read and extract the HTML.”

“This kind of vulnerability could be exploited by an attacker
sending an email with JavaScript in it. The server escapes that
JavaScript and does not see it because it’s within an iframe. When
delivered, the mail client automatically undoes the escaping, and
the JavaScript runs on the client device. Bingo – remote code
execution,” Appleby explains.

“This code can do whatever the attacker desires, up to and
including stealing information and/or sending data back out. An
attacker can send you an email and just by you reading it, they
could steal the contents of your inbox. Weaponized, this can turn
into a very nasty piece of malware.”

Appleby responsibly reported his findings to Microsoft on 10
December 2018, and the company confirmed the vulnerability on 26
March 2019 when he shared a universal PoC with the tech giant.

Microsoft patched the vulnerability and released a fix just 2
days ago—that’s almost 6 months after the initial
vulnerability disclosure. The company says it is currently not
aware of any attacks in the wild related to this issue.

Once again, if your Android device is not yet updated
automatically, you are advised to update your Outlook app from
Google Play Store manually.

References

^{^}
remote code execution vulnerability
(thehackernews.com)
^{^}
Bryan Appleby
(twitter.com)
^{^}
blog post
(www.f5.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.

PoC Released for Outlook Flaw that Microsoft Patched 6 Month After Discovery

References

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