Cyber thieves are making use of DocuSign's Envelopes API to send fake invoices in good faith, complete with names that are giveaways of well-known brands such as Norton and PayPal. Because these messages are sent from a verified domain - namely DocuSign's - they go past traditional email security methods and therefore sneak through undetected as malicious messages.
How It Works
DocuSign is an electronic signing service that the user often provides for sending, signing, and managing documents in a digital manner. Using the envelopes API within its eSignature system, document requests can be sent out, signed, and tracked entirely automatically. Conversely, attackers discovered how to take advantage of this API, where accounts set up for free by paying customers on DocuSign are available to them, giving them access to the templates and the branding feature. They now can create fake-looking invoices that are almost indistinguishable from official ones coming from established companies.
These scammers use the "Envelopes: create" function to send an enormous number of fake bills to a huge list of recipients. In most cases, the charges in the bill are very realistic and therefore appear more legitimate. In order to get a proper signature, attackers command the user to "sign" the documents. The attackers then use the signed document to ask for payment. In some other instances, attackers will forward the "signed" documents directly to the finance department to complete the scam.
Mass Abuse of the DocuSign Platform
According to the security research firm Wallarm, this type of abuse has been ongoing for some time. The company noted that this mass exploitation is exposed by DocuSign customers on online forums as users have marked complaints about constant spamming and phishing emails from the DocuSign domain. "I'm suddenly receiving multiple phishing emails per week from docusign.net, and there doesn't seem to be an obvious way to report it," complained one user.
All of these complaints imply that such abuse occurs on a really huge scale, which makes the attacker's spread of false invoices very probably done with some kind of automation tools and not done by hand.
Wallarm already has raised the attention of the abuse at DocuSign, but it is not clear what actions or steps, if any, are being taken by DocuSign in order to resolve this issue.
Challenges in Safeguarding APIs Against Abuse
Such widespread abuse of the DocuSign Envelopes API depicts how openness in access can really compromise the security of API endpoints. Although the DocuSign service is provided for verified businesses to utilise it, the attack teams will buy valid accounts and utilize these functions offered by the API for malicious purposes. It does not even resemble the case of the DocuSign company because several other companies have had the same abuses of their APIs as well. For instance, hackers used APIs to search millions of phone numbers associated with Authy accounts to validate them, scraping information about millions of Dell customers, matching millions of Trello accounts with emails, and much more.
The case of DocuSign does show how abuses of a platform justify stronger protections for digital services that enable access to sensitive tools. Because these API-based attacks have become so widespread, firms like DocuSign may be forced to consider further steps they are taking in being more watchful and tightening the locks on the misuses of their products with regards to paid accounts in which users have full access to the tools at their disposal.
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