Exim is a widely deployed mail transfer agent; a privilege-escalation bug in Exim can impact many internet mail servers and requires broad sysadmin attention.
CVE-2026-66140
Exim directory traversal in queue-name allows file access and privilege escalation
Is CVE-2026-66140 being exploited?
Not confirmed. CVE-2026-66140 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.26% probability of exploitation in the next 30 days.
How severe is CVE-2026-66140?
CVE-2026-66140 is rated High with a CVSS score of 8.4. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-66140?
Yes. A fix has been recorded for CVE-2026-66140. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-66140 affect?
CVE-2026-66140 affects Exim < 4.99.5, Unix/Linux mail servers running Exim. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-66140?
Upgrade Exim to 4.99.5+ immediately; restrict access and review logs/credentials.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Crafted queue-name causes directory traversal, letting attackers read files outside the spool and escalate privileges (potential root) on Exim hosts.
Immediate action required
- affected>= 4.88 and < 4.99.5
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.