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May 14, 2024

Protecting Your Data: Lessons from the “Dropbox Sign” API and OAuth Breach

Safeguarding Against API Key and OAuth Token Theft

One of the risks of using an expanding cadre of critical online SaaS platforms is that these vendors are routinely attacked by sophisticated hackers.  The largest and most successful vendors, like Dropbox, are attacked more often, with more sophistication, than just about any other type of SaaS vendor. Recent, they fell victim to a breach of their “Dropbox Sign” service offering (formerly “Hello Sign”).

In this article, we’ll look at how attackers got hold of API keys and OAuth tokens, what they gained access to (or didn’t?!), and share some practical tips to help keep your data safe.

Understanding the Dropbox Sign-Breach Incident

The Dropbox Sign breach incident highlighted vulnerabilities in the security infrastructure of their widely used cloud storage service. Their investigation revealed that an unauthorized party managed to access a tool used for configuring Dropbox Sign automatically (Yikes!). A hacker was able to compromise a service account within Sign’s backend service. This is a type of account designated for executing applications and managed access to Dropbox. Consequently, this service account had permissions to perform various actions within Sign’s production environment. The threat actor used this access to gain entry into Dropbox’s customer database (and possibly more!).

Attackers managed to infiltrate Dropbox’s systems, gaining unauthorized access to API keys and OAuth tokens. These cryptographic credentials are instrumental in facilitating secure communication between different applications and services.
By obtaining API keys and OAuth tokens, attackers can impersonate legitimate users or applications, potentially gaining access to sensitive data and compromising the integrity of systems connected to the breached service. The repercussions of such breaches extend far beyond individual accounts, impacting businesses, organizations, and even the broader digital ecosystem.

Who was impacted and What Data was Potentially Stolen

This incident was confined to the Dropbox Sign infrastructure and did not affect any other Dropbox products. If you were not enrolled in Dropbox Sign, then what we know at the moment from Dropbox, is that your data and account is/was safe. 

The hacker did managed to get hold of various Dropbox Sign customer details, like email addresses, usernames, phone numbers, and encrypted passwords. They have also gained access to general account preferences and some authentication details such as API keys, OAuth tokens, and multi-factor authentication information.

Dropbox’s current stance is that there is no evidence suggesting the threat actor(s) accessed the contents of any Dropbox users’ accounts including agreements, templates, or their payment information.

What are API Keys and OAuth Tokens?

API keys and OAuth tokens are cryptographic credentials used to authenticate and authorize access to web services and APIs. Both serve as security measures to ensure that only authorized entities can access protected resources.

  • API Keys: API (Application Programming Interface) keys are unique identifiers assigned to developers or applications to authenticate and control access to an API. They act as a form of authentication, allowing the API provider to identify and track the usage of their services by specific users or applications.
  • OAuth Tokens: OAuth (Open Authorization) tokens are tokens issued by an authorization server to grant permissions for accessing protected resources on behalf of a user. OAuth is commonly used in scenarios where a third-party application needs to access a user’s data stored on a different service without requiring the user to share their credentials directly. OAuth tokens represent the user’s consent to allow the third-party application to access their data, and they are used to authenticate API requests on the user’s behalf.

How Attackers Stole API Keys and OAuth Tokens

The methods employed by attackers to steal API keys and OAuth tokens can vary, ranging from sophisticated cyber attacks to social engineering tactics. In the case of the Dropbox Sign Breach, specific details regarding the attack vector have not been  publicly disclosed, due to the ongoing investigation. However, common techniques utilized by attackers include:

  1. Exploiting Vulnerabilities: Attackers may exploit security vulnerabilities present in the target system or application to gain unauthorized access. This could involve leveraging known vulnerabilities in software components or exploiting misconfigurations in server settings.
  2. Phishing Attacks: Phishing attacks involve tricking users into divulging sensitive information, such as usernames, passwords, or cryptographic credentials. Attackers may craft deceptive emails or websites designed to mimic legitimate services, thereby luring unsuspecting users into providing their credentials.
  3. Malicious Insider Threats: In some cases, malicious insiders with privileged access to systems may abuse their positions to steal API keys and OAuth tokens. Insider threat pose a significant challenge to organizations, as they often possess intimate knowledge of the system’s inner workings.

Fighting Against API Key and OAuth Token Theft

Mitigating the risk of API key and OAuth token theft requires a multi-faceted approach encompassing technical, procedural, and educational measures. Consider implementing the following strategies to bolster your organization’s defenses:

  1. Regular Security Audits: Conduct comprehensive security audits to identify and address vulnerabilities in your systems and applications. Regularly review access controls, encryption mechanisms, and authentication protocols to ensure robust security posture.
  2. Strong Authentication Mechanisms: Implement multi-factor authentication (MFA) to add an extra layer of security to user accounts. MFA requires users to provide additional proof of identity, such as a one-time passcode sent to their mobile device, in addition to their regular credentials.
  3. User Education and Awareness on Phishing: Educate users about the importance of safeguarding their credentials and recognizing phishing attempts. The skill to identify and steer clear of phishing emails is an essential aspect of cyber literacy for everyone online. Providing training sessions and awareness campaigns, such as CyberHoot’s patent-pending phishing simulations to empower users to identify and report suspicious activities. 
  4. Risk Management: Develop a customized Risk Management Framework to suit your organization’s requirements, encompassing procedures for identifying, evaluating, and addressing risks alongside other cybersecurity threats.


When organizations take proactive steps to strengthen their cybersecurity and follow these best practices, they can better protect against breaches including ones like the Dropbox API key and OAuth token theft event. The Dropbox Sign Breach incident is yet another reminder that hackers are after our sensitive data and we need to build cyber resilience into everything we do online. By working together we can create a safer and more secure digital environment for all.

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