CVE-2019-16928: Exim Out-of-bounds Write Vulnerability

100

Patch now

CRITICAL 9.8EXPLOITEDREMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2019-16928 is a critical-severity flaw (CVSS 9.8) affecting exim, ubuntu linux, debian linux, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	41.6% (top 1%)
CISA exploited list	Yes, fix due 2022-03-17
Weakness	CWE-787
Published	2019-09-27
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: canonical · debian · exim · fedoraproject

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2019-09-27 21:15 UTCPublished CVE record published
2022-03-03Exploited Added to the CISA Known Exploited Vulnerabilities list
2022-03-17Deadline CISA due date for US federal agencies to patch
2026-06-17 02:22 UTCUpdated Record last modified

exim exim UPGRADE

Affected: >= 4.92 and <= 4.92.2

Fixed in: newer than 4.92.2

Safe to downgrade to: a release before 4.92

1. Check installed version

apt-cache policy exim || rpm -q exim || exim --version

2. UPGRADE to newer than 4.92.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade exim

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade exim

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 4.92 (Debian / Ubuntu)

apt-cache madison exim sudo apt install exim=<VERSION_BEFORE_4.92> sudo apt-mark hold exim

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list exim sudo dnf downgrade exim-<VERSION_BEFORE_4.92> sudo dnf versionlock add exim

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

canonical ubuntu linux MITIGATE

Affected: 19.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 19.04

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

fedoraproject fedora MITIGATE

Affected: 29 · 30 · 31

Fixed in: no fixed release known

Safe to downgrade to: a release before 29

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora ELN · python-discovery · FIXED · 1.9.0-1.eln159 · FEDORA-2026-7a881c0c99 · source

sudo dnf upgrade --advisory=FEDORA-2026-7a881c0c99

Fedora 46 · pipx · FIXED · 1.18.11-1.fc46 · FEDORA-2026-443a765287 · source

sudo dnf upgrade --advisory=FEDORA-2026-443a765287

Debian 12 · exim4 · FIXED · 4.92.2-3

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.92.2-3" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · exim4 · FIXED · 4.92.2-3

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.92.2-3" && echo PATCHED || echo STILL-VULNERABLE

RHEL 5 · exim · NOT AFFECTED

Alpine 3.20 · exim · FIXED · exim-4.92.2-r1

apk add --upgrade exim apk info -v exim

Alpine 3.21 · exim · FIXED · exim-4.92.2-r1

apk add --upgrade exim apk info -v exim

Alpine 3.22 · exim · FIXED · exim-4.92.2-r1

apk add --upgrade exim apk info -v exim

Alpine 3.23 · exim · FIXED · exim-4.92.2-r1

apk add --upgrade exim apk info -v exim

Amazon Linux 1 · see advisory · FIXED · ALAS-2019-1310 · source

sudo yum update --advisory=ALAS-2019-1310

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2019-16928?

exim: upgrade to newer than 4.92.2; ubuntu linux: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-16928 being exploited?

Yes. CVE-2019-16928 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2019-16928 affect?

CVE-2019-16928 affects exim, ubuntu linux, debian linux. Severity is critical (CVSS 9.8). Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command.

How urgent is CVE-2019-16928?

Priority 100/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Ubuntu vulnerabilities · Debian vulnerabilities · Exim vulnerabilities

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References

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