PayPal flaw allowed hackers to send malicious emails

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)

Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.