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CVE-2019-18988TeamViewer Desktop Bypass Remote Login Vulnerability

Patch nowHigh7.0Exploited, CISA due date 2022-05-03EPSS 4.7%, higher than 92% of scored CVEs

CVE-2019-18988 is a weak password requirements in TeamViewer Desktop, rated high (7.0 on CVSS 3.1).

Why this priority: Exploited in the wild: listed in CISA's KEV catalog.

Published · Updated · NVD status: Analyzed

What it is

Weak passwords are accepted.

How it is reached

An attacker can exploit it by someone who can already run code or sign in on the machine, with an ordinary user account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.

What an attacker gains

A successful attack can read the data it protects, change data or behaviour and take it offline. In practice, this kind of flaw lets an attacker act as a signed-in user, or an administrator, without valid credentials.

Is it being exploited?

CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-03: it is being exploited in the wild. EPSS estimates a 4.7% chance of exploitation activity in the next 30 days, higher than 92% of scored CVEs.

What to do

  1. Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2022-05-03.
  2. No fixed version is listed yet. Find every place TeamViewer Desktop runs, watch the references for a fix, and plan a replacement if it is no longer supported.
  3. Limit who can run code or sign in on the hosts that run it.
  4. Check exposed instances for signs of compromise, not only for the version.

Description from NVD

TeamViewer Desktop through 14.7.1965 allows a bypass of remote-login access control because the same key is used for different customers' installations. It used a shared AES key for all installations since at least as far back as v7.0.43148, and used it for at least OptionsPasswordAES in the current version of the product. If an attacker were to know this key, they could decrypt protect information stored in the registry or configuration files of TeamViewer. With versions before v9.x , this allowed for attackers to decrypt the Unattended Access password to the system (which allows for remote login to the system as well as headless file browsing). The latest version still uses the same key for OptionPasswordAES but appears to have changed how the Unattended Access password is stored. While in most cases an attacker requires an existing session on a system, if the registry/configuration keys were stored off of the machine (such as in a file share or online), an attacker could then decrypt the required password to login to the system.

What this means for your architecture.

A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.

Components it touches

  • Sign-in, session and token handling. The flaw sits between anonymous callers and authenticated sessions.
  • Identity providers and SSO. The flaw sits between anonymous callers and authenticated sessions.

Trust boundaries in play

  • Host boundary. The attacker needs a foothold on the machine first; the flaw turns a small foothold into a bigger one.
  • Between anonymous callers and authenticated sessions. An attacker who crosses it can act as a signed-in user, or an administrator, without valid credentials.

Questions to answer about your own systems

  • Where does TeamViewer Desktop run in your systems, and at which version?
  • Which of those hosts also run code or users you do not fully trust?
  • What can it reach once compromised: which data stores, secrets and services?
See how Veriom maps an architectureTake the interactive tour

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Exploits and proofs of concept

Sources

  • CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
  • Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
  • Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
  • Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.