Threats / Exim / CVE-2018-6789
CVE-2018-6789
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Exim vulnerability
Exim contains a buffer overflow in the base64d function of its SMTP listener, enabling remote code execution without authentication.
Verdict
Today item, not a backlog item.
A remote, unauthenticated attacker can trigger a buffer overflow by sending specially crafted SMTP input to the base64 decoder, achieving arbitrary code execution on the mail server with the privileges of the Exim process.
CISA KEV Yes · 2021-11-033Ransomware use Flagged3EPSS 0.82238 (verify live)4Exploit Weaponized · public PoC5
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Fully weaponized — public exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
6 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.82238 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Exim, Exim. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-119 Memory Buffer Bounds Error — weakness family: Memory safety.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious SMTP message with oversized base64-encoded payload to overflow the decoder buffer.
Business
The mail server becomes compromised, exposing all email data and enabling lateral movement into the organization's network.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I execute arbitrary commands on the compromised Exim process to establish persistence and deploy ransomware.
Business
Critical business systems are encrypted and held for ransom, halting operations and triggering incident response costs.
3
Lateral reach — past segmentation narrative 3
Attacker
I use the mail server as a pivot point to access internal systems and exfiltrate sensitive data.
Business
Confidential information is stolen, resulting in regulatory fines, reputational damage, and customer trust erosion.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05