CVE-2022-1834: Braille Pattern Blank Space Character Exploit in Thunderbird Email Client

CVE-2022-1834 is a critical vulnerability discovered in Thunderbird email client versions below 91.10. The vulnerability allows an attacker to forge the sender's email address by leveraging a Braille Pattern Blank space character. This misrepresentation of the sender's identity can lead to severe phishing attacks and successful email spoofing campaigns. This article will provide the necessary exploit details, code snippet, and original references to understand and mitigate this vulnerability.

Exploit Details

When the Thunderbird email client displays an email sender's name, it includes special characters like the Braille Pattern Blank space character (U+280). If the sender name contains multiple instances of this character, Thunderbird would display all the spaces without truncating them. This behavior can be exploited by an attacker to forge an email with a digital signature that appears to be from an arbitrary sender chosen by the attacker.

In this exploit, the attacker creates an email with a sender name that starts with a false email address, followed by many Braille space characters (U+280). Consequently, the attacker's actual email address remains hidden from the recipient's view. Since Thunderbird verifies the digital signature by comparing the invisible sender address with the signature's email address, a trusted signing key or certificate would make the email appear as if it has a valid digital signature.

Here's a simple snippet to demonstrate the exploit

From: "example@example.com‌⠁⠈⡀⢠⠰⡀⠁⠉
                      attacker@evil.com"
Subject: Important information
Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="signed"

--signed
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable

Hello,
This email is showing synthesized false email address.
Please check the sender info very carefully.

--signed
Content-Type: application/pkcs7-signature; name=smime.p7s
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7s

[... Base64-encoded digital signature ...]

Note that the From field uses the Braille Pattern Blank space character multiple times to push the attacker's actual email address out of the recipient's view, thus making it appear as if the email is sent from 'example@example.com' rather than 'attacker@evil.com.'

For more details about this vulnerability, you can refer to the following sources

1. Mozilla Foundation Security Advisory 2023-16: This official security advisory from the Mozilla Foundation provides an overview of the CVE-2022-1834 vulnerability, along with other vulnerabilities affecting Thunderbird email client.
2. CVE-2022-1834 Record on the NIST NVD: The National Vulnerability Database (NVD) provides additional information about this vulnerability, its impact, and other technical details.

Mitigation

To protect yourself against this vulnerability, it is vital to update your Thunderbird email client to the latest version (91.10 or later). Regularly check for updates to the Thunderbird email client and ensure that security patches are applied timely. Additionally, always be cautious of suspicious sender information in emails and pay close attention to the signing key or certificate's validity and authenticity.

Conclusion

CVE-2022-1834 demonstrates the potential risks associated with the manipulation of special characters in email clients like Thunderbird. It is crucial to understand these risks, apply necessary security patches, and practice vigilance when handling emails, especially those with digitally signed content.

Timeline

Published on: 12/22/2022 20:15:00 UTC
Last modified on: 12/29/2022 16:38:00 UTC