Is CVE-2026-40686 in the CISA KEV catalog?

No. CVE-2026-40686 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-40686?

CVE-2026-40686 has a CVSS v3 base score of 3.7 (LOW).

What is the EPSS score for CVE-2026-40686?

CVE-2026-40686 has an EPSS score of 0.25% (16th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-40686?

Upgrade exim4 on debian 12 to 4.96-15+deb12u9 or later. Fixes are available for 7 affected products.

CVE & CISA-KEV Catalog

CVE-2026-40686

LOW

3.7

CVSS v3

NVD

Description

In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing characters are present (malformed UTF-8 header data). Information might be divulged within an error message produced during handling of an unrelated e-mail message.

CWE-125Out-of-bounds Read

How to fix

Remediation Available

exim4Debian

Fixed in:4.96-15+deb12u9CVE-2026-40686

Fixed in:4.98.2-1+deb13u2CVE-2026-40686

Fixed in:4.99.2-1CVE-2026-40686

exim4Ubuntu

Fixed in:4.82-3ubuntu2.4+esm9USN-8382-1

Fixed in:4.86.2-2ubuntu2.6+esm9USN-8382-1

Fixed in:4.90.1-1ubuntu1.10+esm6USN-8382-1

Fixed in:4.93-13ubuntu1.12+esm1USN-8382-1

Fixed in:4.95-4ubuntu2.7USN-8228-1

Fixed in:4.97-4ubuntu4.4USN-8228-1

Fixed in:4.98.2-1ubuntu2.1USN-8228-1

exim4-baseUbuntu

Fixed in:4.82-3ubuntu2.4+esm9USN-8382-1

Fixed in:4.86.2-2ubuntu2.6+esm9USN-8382-1

Fixed in:4.90.1-1ubuntu1.10+esm6USN-8382-1

Fixed in:4.93-13ubuntu1.12+esm1USN-8382-1

Fixed in:4.95-4ubuntu2.7USN-8228-1

Fixed in:4.97-4ubuntu4.4USN-8228-1

Fixed in:4.98.2-1ubuntu2.1USN-8228-1

exim4-daemon-heavyUbuntu

Fixed in:4.82-3ubuntu2.4+esm9USN-8382-1

Fixed in:4.86.2-2ubuntu2.6+esm9USN-8382-1

Fixed in:4.90.1-1ubuntu1.10+esm6USN-8382-1

Fixed in:4.93-13ubuntu1.12+esm1USN-8382-1

exim4-daemon-lightUbuntu

Fixed in:4.82-3ubuntu2.4+esm9USN-8382-1

Fixed in:4.86.2-2ubuntu2.6+esm9USN-8382-1

Fixed in:4.90.1-1ubuntu1.10+esm6USN-8382-1

Fixed in:4.93-13ubuntu1.12+esm1USN-8382-1

exim4-devUbuntu

Fixed in:4.82-3ubuntu2.4+esm9USN-8382-1

Fixed in:4.86.2-2ubuntu2.6+esm9USN-8382-1

Fixed in:4.90.1-1ubuntu1.10+esm6USN-8382-1

Fixed in:4.93-13ubuntu1.12+esm1USN-8382-1

eximon4Ubuntu

Fixed in:4.82-3ubuntu2.4+esm9USN-8382-1

Fixed in:4.86.2-2ubuntu2.6+esm9USN-8382-1

Fixed in:4.90.1-1ubuntu1.10+esm6USN-8382-1

Fixed in:4.93-13ubuntu1.12+esm1USN-8382-1

Fixed in:4.95-4ubuntu2.7USN-8228-1

Fixed in:4.97-4ubuntu4.4USN-8228-1

Fixed in:4.98.2-1ubuntu2.1USN-8228-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityNone

AvailabilityNone

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

Exploit Intelligence

0.25%probability of exploitation in 30 days

16thpercentile

Low risk: more likely to be exploited than 16% of all known CVEs.

References

Patch1

code.exim.org

Vendor Advisory1

exim.org

Third-Party Advisory1

openwall.com

Other references1

exim.org

Related Vulnerabilities

Other CWE-125 (Out-of-bounds Read) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2014-0160	High	7.5	100%	KEV	Fix
CVE-2025-5777	High	7.5	100%	KEV + Ransom	Fix
CVE-2021-4034	High	7.8	95%	KEV	Fix
CVE-2023-21769	High	7.5	92%	-	Fix
CVE-2023-49285	High	8.6	89%	-	Fix
CVE-2020-8794	Critical	9.8	89%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-01.