The S/MIME specification allows a Cipher Block Chaining (CBC) malleability-gadget attack that can indirectly lead to plaintext exfiltration, aka EFAIL.
https://www.synology.com/support/security/Synology_SA_18_22
https://twitter.com/matthew_d_green/status/996371541591019520
https://pastebin.com/gNCc8aYm
https://news.ycombinator.com/item?id=17066419
http://www.securityfocus.com/bid/104165
Source: Mitre, NVD
Published: 2018-05-16
Updated: 2024-11-21
Base Score: 4.3
Vector: CVSS2#AV:N/AC:M/Au:N/C:P/I:N/A:N
Severity: Medium
Base Score: 5.9
Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS: 0.00424