Pierluigi Paganini March 30, 2016

PayPal has just fixed a security vulnerability that could have been exploited to send malicious emails to users via its platform.

Researchers at security firm Vulnerability Lab have discovered a filter bypass and an application-side input validation vulnerability that allowed attackers to inject malicious code into emails sent by the PayPal platform.

“A persistent input validation & mail encoding web vulnerability has been discovered in the official PayPal Inc online-service web-application. The validation and mail encoding web vulnerability allows remote attackers to inject own malicious script codes to the mail header of the portal mails. ” states the post published by the Vulnerability Lab.

When PayPal users create a new account, they can link it to multiple email addresses. Each email address has to be confirmed by the users by providing a confirmation code sent to the account they want to confirm.

Unfortunately, an attacker could create an  account and insert arbitrary HTML code in the account owner field.

The attack scenario is simple, the attacker links the new account to the victim’s email and insert a malicious code in the account owner name. The platform then sends the a confirmation email to that address of the victims, the message includes the malicious code that would get executed when the victims open the email.

The attack could be very insidious because the emails are sent from the legitimate PayPal platform through the account service[@]paypal.com, for this reason, the email is not detected as spam or malicious by the defense systems.

The above attack scenario could be exploited in phishing campaigns, session hijacking, and to redirect users to certain domains managed by the attackers.

Below a proof-of-concept video published by the experts at the Vulnerability Lab.

Vulnerability Lab reported the issue to PayPal in October 2015, the vulnerability has been fixed this month. The company awarded the researcher Kunz Mejri from Vulnerability Lab with $1,000.

The details of the flaw, for which Kunz Mejri received $1,000, were disclosed on Wednesday.

Pierluigi Paganini

(Security Affairs – PayPal, hacking)