NVD / CVE Program· CNA mitre

CVE-2018-6789: An issue was discovered in the base64d function in the SMTP listener in Exim before 4.90.1.

CriticalCVSS 9.8 · v3.1KEVWeaponized Fix available

Noroxi assessment

Priority: Now (action score 94/100)

CISA has confirmed exploitation in the wild (Nov 3, 2021); it is known to be used in ransomware campaigns. Remediation deadline for US federal agencies: May 3, 2022.
Probability of exploitation in the next 30 days: 82.1% (FIRST EPSS); higher than 99.6% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: exim (Alpine:v3.10) 4.90.1-r0; exim4 (Debian:12) 4.90.1-1; exim4 (Debian:7) 4.80-7+deb7u6.

Patch today or shut off access. Upgrade to exim (Alpine:v3.10) 4.90.1-r0; exim4 (Debian:12) 4.90.1-1; exim4 (Debian:7) 4.80-7+deb7u6 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · CISA KEV · FIRST EPSS

An issue was discovered in the base64d function in the SMTP listener in Exim before 4.90.1. By sending a handcrafted message, a buffer overflow may happen. This can be used to execute code remotely.

Published: Feb 8, 2018
Updated: Jun 16, 2026
EPSS: 82.1% · 99th percentile
CWE: CWE-120

Report tools

JSON

Action score

Now

Patch today or shut off access.

CVSS: 39 / 40 · 9.8 / 10
CISA KEV: 30 / 30 · Listed
EPSS: 25 / 30 · 82.1%

CISA SSVC decision

Exploitation: active
Automatable: yes
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Nov 3, 2021. That signals real attacks, not theory.

Remediation deadline for US federal agencies: May 3, 2022.

Known to be used in ransomware campaigns.

Get told when this record changes

In CISA KEV: exploitation in the wild confirmed
Weaponized exploit exists
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
exim	exim	cpe:2.3:a:exim:exim
debian	debian linux	cpe:2.3:o:debian:debian_linux
canonical	ubuntu linux	cpe:2.3:o:canonical:ubuntu_linux

Using exim? Add it to your stack and be the first to know about CVEs like this one. (Email server)

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

exim eximbefore 4.90.1

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.10	exim	before 4.90.1-r0	4.90.1-r0
Debian:12	exim4	before 4.90.1-1	4.90.1-1
Debian:7	exim4	before 4.80-7+deb7u6	4.80-7+deb7u6
Debian:8	exim4	before 4.84.2-2+deb8u5	4.84.2-2+deb8u5
Debian:9	exim4	before 4.89-2+deb9u3	4.89-2+deb9u3
openSUSE:Leap 15.2	exim	before 4.94.2-lp152.8.3.1	4.94.2-lp152.8.3.1
openSUSE:Tumbleweed	exim	before 4.94.2-4.2	4.94.2-4.2
SUSE:Package Hub 15 SP1	exim	before 4.94.2-bp151.2.4.1	4.94.2-bp151.2.4.1
SUSE:Package Hub 15 SP1	libspf2	before 1.2.10-bp151.4.1	1.2.10-bp151.4.1
SUSE:Package Hub 15 SP2	exim	before 4.94.2-bp152.6.4.1	4.94.2-bp152.6.4.1
SUSE:Package Hub 15 SP2	libspf2	before 1.2.10-bp152.5.1	1.2.10-bp152.5.1

Same product

exim: all records

Other highest-scoring records for the same primary product.

CVE-2019-10149A flaw was found in Exim versions 4.87 to 4.91 (inclusive).KEV
99Now
CVE-2010-4344Heap-based buffer overflow in the string_vformat function in string.c in Exim before 4.70 allows remote attackers to execute arbitrary code…KEV
91Now
CVE-2019-16928Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846.KEV
81Now

Published before and after this one in the same product

← EarlierCVE-2017-16943Nov 25, 2017 · The receive_msg function in receive.c in the SMTP daemon in Exim 4.88 and 4.89 allows remote attackers to execute arbitrary code or cause a…
53Plan
← EarlierCVE-2017-16944Nov 25, 2017 · The receive_msg function in receive.c in the SMTP daemon in Exim 4.88 and 4.89 allows remote attackers to cause a denial of service…
49Plan
Later →CVE-2019-13917Jul 25, 2019 · Exim 4.85 through 4.92 (fixed in 4.92.1) allows remote code execution as root in some unusual configurations that use the ${sort }…
42Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
alpine:exim	4.90.1-r0 · Alpine:v3.10	Package registry (OSV)
debian:exim4	4.90.1-1 · Debian:12	Package registry (OSV)
opensuse:exim	4.94.2-lp152.8.3.1 · openSUSE:Leap 15.2	Package registry (OSV)
suse:exim	4.94.2-bp151.2.4.1 · SUSE:Package Hub 15 SP1	Package registry (OSV)
suse:libspf2	1.2.10-bp151.4.1 · SUSE:Package Hub 15 SP1	Package registry (OSV)

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Evidence

Exploit-DB entry ×2
Proof-of-concept repository on GitHub ×5

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
Source	Kind	Date
Proof-of-concept repository on GitHub	5 repositories	2018-03-16 → 2023-08-05
Exploit-DB entry	remote	2018-10-24
Exploit-DB entry	remote	2018-05-02

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

PublishedFeb 8, 2018
First PoCMar 16, 2018+35 d
CISA KEVNov 3, 2021+1363 d
TodayNov 13, 2026+3200 d

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

git.exim.orgcommit cf3cd30

Not on record for this CVE: EPSS history · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-120 · Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Root cause

When data is copied, the source length is not compared with the size of the destination buffer. Excess data overwrites adjacent memory.

The bug in code

The whole CWE-120 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1char buf[256];
2memcpy(buf, pkt->data, pkt->len);

Fixed

1char buf[256];
2if (pkt->len > sizeof(buf)) {
3  return -EINVAL;
4}
5memcpy(buf, pkt->data, pkt->len);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log (1)

Fix✗ → ✓Sep 28, 2026, 10:47 PM UTC

For records you follow, these changes also arrive as notifications. →

References

openwall.com/lists/oss-security/2018/02/10/2

Show all references (9 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records

Noroxi analysis

What does it mean in your environment?

We use this product, ask for help

Data sources and verification

CNA: mitre

CVE.org (CNA)Oct 21, 2025, 11:45 PM UTC
CISA ADPOct 21, 2025, 11:45 PM UTC
NVDJun 16, 2026, 10:02 PM UTC
FIRST EPSSNov 11, 2026, 12:00 AM UTC
OSV / GHSANov 13, 2026, 3:18 AM UTC
Exploit-DBNov 13, 2026, 3:17 AM UTC
PoC-in-GitHubNov 13, 2026, 3:18 AM UTC

Each line is when that source was last processed for this record.

CVE-2018-6789: An issue was discovered in the base64d function in the SMTP listener in Exim before 4.90.1.

Noroxi assessment

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Affected systems

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Affected versions

Package-level exposure

Same product

Remediation

Which version to upgrade to

Exploit status

Research context

Timeline

Patch and commit links

Technical details

Attack conditions

If successful

Root cause

The bug in code

Attack context

References