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A set of security bugs that allow spoofed emails to evade standard security measures have been identified. Security researchers dubbed the flaws ‘Mailsploit’. This form of attack allows malicious actors to insert a fake sender name into emails without detection by modern anti-spoofing tools. In selective instances, Mailsploit will also allow malicious code to be run on a victim’s device. There are currently 33 email clients vulnerable to this attack including Apple Mail, Outlook, and Mozilla Thunderbird; for a full list of vulnerable mail clients please see the link below [1].  At the time of publication, only eight client applications have released patches.

 

What should you do about it

  • After completing a business impact review, apply manufacturer updates as they become available.
  • Use PGP for emails to verify the identities of senders and encrypt messages.
  • Ensure users are informed about current phishing threats through awareness programs and training.

 

Additional information

The Mailsploit security bugs allow attackers’ spoofed emails to bypass the anti-spoofing protocol DMARC. The attack is made possible due to improper sanitization of non-ASCII characters in the "From:" field. Some email applications when decoding Internet Message Headers only display strings up to the first null or newline character. This prevents the full email address from being displayed to the user. As such, attackers can insert a null character to obfuscate their real email.   

 

For additional technical details see the link for the original vulnerability report below [2].

[1] https://docs.google.com/spreadsheets/d/1jkb_ZybbAoUA43K902lL-sB7c1HMQ78-fhQ8nowJCQk/htmlview?sle=true

[2] https://www.mailsploit.com/index

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Articles and reports written by eSentire staff and our Threat Intelligence Research Group.

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