CVE-2020-28018
CriticalExim 4 before 4.94.2 allows Use After Free in smtp_reset in certain situations that may be common for builds with OpenSSL.
Published May 7, 2021 · Updated Aug 5, 2026 · Also known as DEBIAN-CVE-2020-28018, UBUNTU-CVE-2020-28018
Key Facts
Patch immediately- CVE-2020-28018 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting Exim, exim4 (debian), exim-greylist (amazon) and 8 more products.
- It is not listed in any known-exploited vulnerabilities catalog. No public exploit code is known.
- EPSS estimates a 56% probability of exploitation in the next 30 days.
- Fixed versions are available, including Exim 4.92-1.27.amzn1, Exim 4.94.2-1, Exim 4.94.2-4.2.
- Brandefense priority: patch immediately, because it is very likely to be exploited soon.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
56%
Higher than 99.0% of all scored CVEs
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
None known
Get the full CVE-2020-28018 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
Description
Exim 4 before 4.94.2 allows Use After Free in smtp_reset in certain situations that may be common for builds with OpenSSL.
Affected Products
54 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| EximExim | See advisory | 4.94.2 |
| exim4debian | See advisory | 4.94.2-1 |
| exim-greylistamazon | See advisory | 4.92-1.27.amzn1 |
| exim-monamazon | See advisory | 4.92-1.27.amzn1 |
| exim-mysqlamazon | See advisory | 4.92-1.27.amzn1 |
Patched Releases
Exim
4.92-1.27.amzn1, 4.94.2-1, 4.94.2-4.2, 4.94.2-bp151.2.4.1, 4.94.2-bp152.6.4.1, 4.94.2-lp152.8.3.1, 4.94.2-r0, 4.94.2
exim-greylist
4.92-1.27.amzn1
exim-mon
4.92-1.27.amzn1
exim-mysql
4.92-1.27.amzn1
exim-pgsql
4.92-1.27.amzn1
exim4
4.90.1-1ubuntu1.8, 4.93-13ubuntu1.5, 4.94.2-1
eximon
4.94.2-4.2, 4.94.2-bp151.2.4.1, 4.94.2-bp152.6.4.1, 4.94.2-lp152.8.3.1
eximstats-html
4.94.2-4.2, 4.94.2-bp151.2.4.1, 4.94.2-bp152.6.4.1, 4.94.2-lp152.8.3.1
libspf2-2
1.2.10-bp151.4.1, 1.2.10-bp152.5.1
libspf2-devel
1.2.10-bp151.4.1, 1.2.10-bp152.5.1
libspf2-tools
1.2.10-bp151.4.1, 1.2.10-bp152.5.1
Timeline
Publicly disclosed
May 7, 2021
Last updated
Aug 5, 2026
Weakness Type
- CWE-416 Use After Free
References
- advisoryhttps://blog.qualys.com/vulnerabilities-research/2021/05/04/21nails-multiple-vulnerabilities-in-exim-mail-server
- advisoryhttps://blog.qualys.com/vulnerabilities-research/2021/05/04/21nails-multiple-vulnerabilities-in-exim-mail-server/
- advisoryhttps://blog.qualys.com/vulnerabilities-research/2021/05/04/21nails-multiple-vulnerabilities-in-exim-mail-server?utm_source=dlvr.it&utm_medium=twitter
- advisoryhttps://github.com/iphelix/dnschef
- advisoryhttps://nvd.nist.gov/vuln/detail/cve-2019-10149
FAQ
Common Questions.
Exim 4 before 4.94.2 allows Use After Free in smtp_reset in certain situations that may be common for builds with OpenSSL.
Affected: Exim; exim4 (debian); exim-greylist (amazon), among others. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including Exim 4.92-1.27.amzn1, Exim 4.94.2-1, Exim 4.94.2-4.2.
Brandefense priority: patch immediately, because it is very likely to be exploited soon.
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