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CVE-2026-66141: Exim Security Vulnerability (CVSS 7.4)

CVE-2026-66141 is a high severity security vulnerability in Exim with a CVSS score of 7.4. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

Last updated: Aug 17, 2026

Quick answer

Direct answer

CVE-2026-66141 is a high severity security vulnerability in Exim with a CVSS score of 7.4. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

Risk scores

CVSS base score
7.4HIGH
EPSS probability
0.14%
Higher than 3 percent of all CVEs
CISA KEV
Not listed
CVSS metricWhat it means
Attack vector (AV:L)Local access needed
Attack complexity (AC:H)High complexity
Privileges required (PR:N)No privileges required
User interaction (UI:N)No user interaction
Scope (S:U)Scope unchanged
Confidentiality (C:H)High confidentiality impact
Integrity (I:H)High integrity impact
Availability (A:H)High availability impact

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

About Exim

CVE-2026-66141 affects Exim, a product from Exim. Before acting, confirm where Exim runs in your estate, who owns it and whether it is reachable from the internet, because exposure decides real risk more than the score alone.

What the flaw is

In plain terms: Exim before 4.99.5 allows .forward privilege escalation because force_command for a pipe transport is mishandled.

Based on its CVSS vector, the flaw needs local or adjacent access, needs no login, and needs no user interaction. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

Affected versions and timeline

FieldDetail
ProductExim
Affected versionsExim before 4.99.5
PublishedJul 24, 2026
Last modifiedAug 17, 2026
Added to CISA KEVNot listed
Assigning CNAcve@mitre.org

How to detect it

  • Inventory every instance of Exim and record the running version against the affected range above.
  • Check external attack surface scans for internet facing instances of the component.
  • Review logs on affected systems for unusual requests, errors or new processes around the vulnerable function.
  • Confirm with an authenticated vulnerability scan once your scanner has a check for this CVE.

How to fix it

  • Apply the fixed version of Exim named in the vendor advisory.
  • If patching must wait, restrict network access to the affected service and put it behind authentication or a web application firewall rule.
  • Rescan after the change to prove the exposure is gone, then close the ticket.

CTEM action plan

CTEM stageWhat to do for this CVE
ScopeAdd every business service that depends on Exim to the current CTEM cycle.
DiscoverFind all instances, including shadow and cloud deployments, and record versions and exposure.
PrioritizeRank using EPSS and CVSS together with asset exposure and business impact.
ValidateConfirm the flaw is reachable and exploitable in your environment and that compensating controls work.
MobilizeAssign the fix to the asset owner with a due date matched to the priority, then verify closure.

CWE References

Technical References

Frequently asked questions

CVE-2026-66141 is a high severity security vulnerability in Exim with a CVSS score of 7.4. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

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