S/MIME: CBC gadget attacks allows to exfiltrate plaintext out of encrypted emails
Published May 16, 2018
5.9
MEDIUMCVSS 3.0
EPSS 4.13%
Description
The S/MIME specification allows a Cipher Block Chaining (CBC) malleability-gadget attack that can indirectly lead to plaintext exfiltration, aka EFAIL.
Affected products
No data.
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No data.
Red Hat Enterprise Linux 6
kdepim
Will not fix
Red Hat Enterprise Linux 6
thunderbird
Not affected
Red Hat Enterprise Linux 7
kdepim
Will not fix
Red Hat Enterprise Linux 7
thunderbird
Not affected
Red Hat Enterprise Linux 8
thunderbird
Not affected
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Enterprise Linux 6 | kdepim | Will not fix | n/a |
| Red Hat Enterprise Linux 6 | thunderbird | Not affected | n/a |
| Red Hat Enterprise Linux 7 | kdepim | Will not fix | n/a |
| Red Hat Enterprise Linux 7 | thunderbird | Not affected | n/a |
| Red Hat Enterprise Linux 8 | thunderbird | Not affected | n/a |
No package ranges for this CVE.
Remediation
Red Hat statement
The research paper talks about use of HTML as a back channel to create an oracle for modified encrypted emails. HTML emails which use external links like "<img href="tla.org/TAG"/>" can cause security issues if they are honored by the MUAs. Due to flaws in MIME parsers many MUAs seem to concatenate decrypted HTML mine parts which makes it easy to plan such snippets in HTML emails. Please refer to https://lists.gnupg.org/pipermail/gnupg-users/2018-May/060315.html about how GnuPG can mitigate this flaw. For Thunderbird, this vulnerability was known as CVE-2018-5162 and resolved in 52.8.
Red Hat mitigation
The easiest way to mitigate this vulnerability is not to use HTML emails. If you really need to use them ensure that MUA clients disable external links embedded in HTML emails. For example in thunderbird email client, Edit->Preferences->Privacy->Disable "Allow remote content in messages".
Metrics
No CVSS v4.0 score for this CVE.
No CVSS v3.1 score for this CVE.
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
1 other source (Red Hat) ▾
CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N
AV:N/AC:M/Au:N/C:P/I:N/A:N
This CVE is not in the KEV list.
No CISA SSVC assessment for this CVE yet.
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
Score over time
2021–2026- EPSS v1
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Percentile over time
- EPSS v1
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Table of values (22 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 4.13% (0.04133) | 90.51th | v5 (v2026.06.15) |
| Jun 15, 2026 | 4.22% (0.04219) | 89.67th | v5 (v2026.06.15) |
| Mar 30, 2025 | 0.42% (0.00424) | 59.28th | v4 (v2025.03.14) |
| Mar 29, 2025 | 1.94% (0.01941) | 72.48th | v4 (v2025.03.14) |
| Mar 17, 2025 | 0.42% (0.00424) | 60.08th | v4 (v2025.03.14) |
| Dec 12, 2024 | 0.52% (0.00523) | 77.66th | v3 (v2023.03.01) |
| May 31, 2024 | 0.52% (0.00523) | 76.84th | v3 (v2023.03.01) |
| Feb 10, 2024 | 0.55% (0.00546) | 76.73th | v3 (v2023.03.01) |
| Oct 7, 2023 | 0.55% (0.00546) | 74.72th | v3 (v2023.03.01) |
| Jul 8, 2023 | 0.44% (0.00443) | 71.41th | v3 (v2023.03.01) |
| May 10, 2023 | 0.47% (0.00470) | 71.94th | v3 (v2023.03.01) |
| May 8, 2023 | 0.39% (0.00392) | 69.35th | v3 (v2023.03.01) |
| Mar 7, 2023 | 0.37% (0.00369) | 68.26th | v3 (v2023.03.01) |
| Mar 6, 2023 | 8.76% (0.08761) | 93.95th | v2 (v2022.01.01) |
| Apr 1, 2022 | 8.76% (0.08761) | 93.42th | v2 (v2022.01.01) |
| Mar 29, 2022 | 8.76% (0.08761) | 83.23th | v2 (v2022.01.01) |
| Feb 20, 2022 | 7.92% (0.07919) | 81.79th | v2 (v2022.01.01) |
| Feb 4, 2022 | 7.22% (0.07216) | 80.48th | v2 (v2022.01.01) |
| Feb 3, 2022 | 7.41% (0.07414) | 83.89th | v1 |
| Jan 6, 2022 | 7.41% (0.07414) | 83.73th | v1 |
| Sep 1, 2021 | 7.41% (0.07414) | 91.41th | v1 |
| Apr 14, 2021 | 7.41% (0.07414) | 0.00th | v1 |
References (10)
- http://www.securityfocus.com/bid/104165 vdb-entryx_refsource_BIDThird Party AdvisoryVDB Entry
- https://access.redhat.com/security/cve/CVE-2017-17689 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1577909 Issue Tracking
- https://efail.de x_refsource_MISCExploitMitigationThird Party Advisory
- https://news.ycombinator.com/item?id=17066419 x_refsource_MISCIssue TrackingThird Party Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2017-17689
- https://pastebin.com/gNCc8aYm x_refsource_MISCThird Party Advisory
- https://twitter.com/matthew_d_green/status/996371541591019520 x_refsource_MISCThird Party Advisory
- https://www.cve.org/CVERecord?id=CVE-2017-17689
- https://www.synology.com/support/security/Synology_SA_18_22 x_refsource_CONFIRMThird Party Advisory
| Link | Providers | Tags |
|---|---|---|
| http://www.securityfocus.com/bid/104165 | vdb-entryx_refsource_BIDThird Party AdvisoryVDB Entry | |
| https://access.redhat.com/security/cve/CVE-2017-17689 | Vendor Advisory | |
| https://bugzilla.redhat.com/show_bug.cgi?id=1577909 | Issue Tracking | |
| https://efail.de | x_refsource_MISCExploitMitigationThird Party Advisory | |
| https://news.ycombinator.com/item?id=17066419 | x_refsource_MISCIssue TrackingThird Party Advisory | |
| https://nvd.nist.gov/vuln/detail/CVE-2017-17689 | ||
| https://pastebin.com/gNCc8aYm | x_refsource_MISCThird Party Advisory | |
| https://twitter.com/matthew_d_green/status/996371541591019520 | x_refsource_MISCThird Party Advisory | |
| https://www.cve.org/CVERecord?id=CVE-2017-17689 | ||
| https://www.synology.com/support/security/Synology_SA_18_22 | x_refsource_CONFIRMThird Party Advisory |
Change history (0)
No recorded changes yet.