CVE-2018-18509

Severity: medium (CVSS 5.3 v3.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2019-04-26 · updated 2026-06-17
Weakness: CWE-347

Description

A flaw during verification of certain S/MIME signatures causes emails to be shown in Thunderbird as having a valid digital signature, even if the shown message contents aren't covered by the signature. The flaw allows an attacker to reuse a valid S/MIME signature to craft an email message with arbitrary content. This vulnerability affects Thunderbird < 60.5.1.

Affected products

Mozilla Thunderbird: before 60.5.1 — fixed in 60.5.1

How to fix

Upgrade to a fixed version: Mozilla Thunderbird 60.5.1. Check the vendor advisory for mitigations.

References

http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00043.html
http://packetstormsecurity.com/files/152703/Johnny-You-Are-Fired.html
http://seclists.org/fulldisclosure/2019/Apr/38
http://www.openwall.com/lists/oss-security/2019/04/30/4
https://access.redhat.com/errata/RHSA-2019:1144
https://bugzilla.mozilla.org/show_bug.cgi?id=1507218
https://github.com/RUB-NDS/Johnny-You-Are-Fired
https://github.com/RUB-NDS/Johnny-You-Are-Fired/blob/master/paper/johnny-fired.pdf
https://www.mozilla.org/security/advisories/mfsa2019-06/
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00043.html
http://packetstormsecurity.com/files/152703/Johnny-You-Are-Fired.html
http://seclists.org/fulldisclosure/2019/Apr/38

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