CVE-2026-45185: Exim before 4.99.3, in certain GnuTLS configurations, has a remotely reachable use-after-free in the BDAT body

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2026-45185 is a critical-severity flaw (CVSS 9.8) affecting exim. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Exim before 4.99.3, in certain GnuTLS configurations, has a remotely reachable use-after-free in the BDAT body parsing path. It is triggered when a client sends a TLS close_notify mid-body during a CHUNKING transfer, followed by a final cleartext byte on the same TCP connection. This can lead to heap corruption. An unauthenticated network attacker exploiting this vulnerability could execute arbitrary code.

Why this priority

Critical severity
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

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	1.3% (top 30%)
CISA exploited list	No
Weakness	CWE-416
Published	2026-05-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: exim

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

Am I affected?

Timeline

2026-05-12 20:16 UTCPublished CVE record published
2026-06-17 10:51 UTCUpdated Record last modified

exim exim UPGRADE

Affected: >= 4.97 and < 4.99.3

Fixed in: 4.99.3

Safe to downgrade to: a release before 4.97

1. Check installed version

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

2. UPGRADE to 4.99.3 (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 4.97 (Debian / Ubuntu)

apt-cache madison exim sudo apt install exim=<VERSION_BEFORE_4.97> 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_4.97> 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.

Exact fixes by distribution

Fedora 46 · proftpd · FIXED · 1.3.9e-1.fc46 · FEDORA-2026-fc0d87d66e · source

sudo dnf upgrade --advisory=FEDORA-2026-fc0d87d66e

Ubuntu 22.04 · exim4 · FIXED · 4.95-4ubuntu2.8

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.95-4ubuntu2.8" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 24.04 · exim4 · FIXED · 4.97-4ubuntu4.5

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.97-4ubuntu4.5" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 25.10 · exim4 · FIXED · 4.98.2-1ubuntu2.2

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.98.2-1ubuntu2.2" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 20.04 · exim4 · FIXED · 4.93-13ubuntu1.12+esm1

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.93-13ubuntu1.12+esm1" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · exim4 · FIXED · 4.96-15+deb12u9

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.96-15+deb12u9" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · exim4 · FIXED · 4.98.2-1+deb13u2

sudo apt update && sudo apt install --only-upgrade exim4 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' exim4)" ge "4.98.2-1+deb13u2" && echo PATCHED || echo STILL-VULNERABLE

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: MJ-bin/POC_CVE-2026-45185 (4 stars)
GitHub PoC: liamromanis101/Dead.Letter-CVE-2026-45185 (2 stars)
GitHub PoC: materaj2/cve-2026-45185-detection-script (0 stars)
Write-up: xbow.com/blog/dead-letter-cve-2026-45185-xbow-found-rce-exim

Verify at the official source NVD · CVE Program · 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-2026-45185?

exim: upgrade to 4.99.3. Exact commands for each OS are on this page.

Is CVE-2026-45185 being exploited?

CVE-2026-45185 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-45185 affect?

CVE-2026-45185 affects exim. Severity is critical (CVSS 9.8). Exim before 4.99.3, in certain GnuTLS configurations, has a remotely reachable use-after-free in the BDAT body parsing path. It is triggered when a client sends a TLS close_notify mid-body during a CHUNKING transfer, followed by a final cle

How urgent is CVE-2026-45185?

Priority 60/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Software pages

Exim vulnerabilities · GnuTLS vulnerabilities

Related CVEs

CVE-2026-94054 HIGH 7.0 UPGRADE Exim before 4.100.1, when Proxy-Protocol is used with an attacker-controlled proxy, has an out-of-bounds write
CVE-2026-94055 LOW 3.7 UPGRADE Exim before 4.100.1, when certain non-default TLS settings are used with GnuTLS, has a use-after-free.
CVE-2026-94056 HIGH 7.5 UPGRADE Exim before 4.100.1, when Proxy-Protocol is used with an attacker-controlled proxy, allows attackers to read c
CVE-2026-94057 MEDIUM 4.0 UPGRADE Exim before 4.100.1 allows SMTP smuggling in which the received message does not match any sent message, and i
CVE-2026-66141 HIGH 7.4 UPGRADE Exim before 4.99.5 allows .forward privilege escalation because force_command for a pipe transport is mishandl

References

← Back to latest CVEs