high CVSS 8.4 EPSS 0.39%

CVE-2026-66140·Exim vulnerability

Exim before 4.99.5 allows directory traversal to access files outside of the spool area, and consequently gain privileges, because arguments related to queue-name are mishandled.

Severity
high
Software
Exim
Fixed in
4.99.5
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.39% — higher than 31% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-66140 scores 8.4 on CVSS, so a successful attack would be serious — but at 0.39%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 4.99.5

Fixed in: 4.99.5

How to fix this CVE

Exim versions prior to 4.99.5 contain a local privilege escalation flaw in queue-name argument handling that permits attackers to traverse outside the mail spool directory and access sensitive files. Immediately upgrade Exim to version 4.99.5 or later to patch this vulnerability. Review file permissions on your Exim spool directory and ensure proper access controls are in place to minimize local attack surface.

sudo dnf update exim

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed Exim version: exim -v | grep version
  2. Verify spool directory permissions: ls -ld /var/spool/exim4 (should be 700 or 750 owned by Debian-exim)
  3. Search for queue-name traversal attempts in mail logs: grep -E '(\.\.|\.\./|queue.*name)' /var/log/exim4/mainlog
  4. Confirm patch applied by running: exim -v and verifying version is 4.99.5 or greater

FAQ

What is CVE-2026-66140?

This vulnerability is a local privilege escalation in Exim's queue-name argument processing that allows an attacker with local system access to bypass spool directory restrictions and read or modify files outside the intended mail queue area.

Is CVE-2026-66140 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available, but it should still be patched promptly due to its high severity rating.

What versions of Exim are affected by CVE-2026-66140?

All Exim versions before 4.99.5 are affected. The exact earliest vulnerable version is unknown, but organizations running any version below 4.99.5 should upgrade immediately.

How do I check if my server is vulnerable to CVE-2026-66140?

Run `exim -v` and compare the version number to 4.99.5. If your version is lower, your system is vulnerable. You can also use: `dpkg -l | grep exim` on Debian/Ubuntu or `rpm -q exim` on RHEL/CentOS.

Does Defensia detect CVE-2026-66140?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Exim is installed on a monitored server, CVE-2026-66140 will appear in your dashboard with remediation steps.

Related Exim CVEs

CVE-2010-4344CVSS 10Heap-based buffer overflow in the string_vformat function in string.c in Exim before 4.70 allows remote attackers to execute arbitrary code via an SMTP session that includes two MAIL commands in conjunction with a large message containing crafted headers, leading to improper rejection logging.
CVE-2019-16928CVSS 10Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command.
CVE-2019-10149CVSS 10A flaw was found in Exim versions 4.87 to 4.91 (inclusive). Improper validation of recipient address in deliver_message() function in /src/deliver.c may lead to remote command execution.
CVE-2018-6789CVSS 10An 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.
CVE-2026-45185CVSS 9.8Exim 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.

References

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