CVE-2017-7829

What it actually does

The vulnerability allows spoofing of the displayed sender address in emails by embedding a null character in the display string, which suppresses the real sender address from being shown to the recipient.

Why it matters to the business

Attackers can impersonate trusted organizations or individuals via email, increasing the success rate of phishing and social engineering campaigns that lead to credential theft or malware delivery.

How an attack unfolds

An attacker crafts an email message with a From header containing an arbitrary display name followed by a null byte and the real address; when rendered in the vulnerable client the null byte terminates display of the real address, showing only the spoofed name to the recipient.

How to fix it

Upgrade Mozilla Thunderbird to version 52.5.2 or later on all affected systems.

How to confirm the fix worked

Verify installed Thunderbird version is 52.5.2 or newer; test by sending an email containing a null byte in the From display string and confirm the real address is now visible.

Typical attack path

1. Craft an email with a null byte preceding the real sender address in the From display string
2. Send the message to the target recipient
3. Recipient client renders only the spoofed sender address

How to detect it

Inspect incoming email headers for null bytes in the From field or unusual display-name patterns; review mail server logs and client message stores for messages that triggered the spoofing condition.

• From:.*\x00
• null byte in email From header display string

What your security team should do

• Immediately update all Thunderbird installations to 52.5.2 or newer
• Enable SPF, DKIM and DMARC on outbound mail domains to reduce spoofing success
• Train users to treat unexpected email requests with caution regardless of displayed sender