How severe is CVE-2026-40684?

CVE-2026-40684 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-40684 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40684?

CVE-2026-40684 affects Exim. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-40684?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40684 have an EU (EUVD) identifier?

Yes. CVE-2026-40684 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-26442.

When was CVE-2026-40684 published?

CVE-2026-40684 was published on 2026-04-30 and last updated on 2026-06-17.

CVE-2026-40684

CVE-2026-40684 is a medium-severity vulnerability in Exim with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-684.

Key facts

Severity: Medium (CVSS 3.x base score 5.9)
EPSS exploit prediction: 0% (28th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-26442
Weakness: CWE-684
Affected product: Exim
Published: 2026-04-30
Last modified: 2026-06-17

Description

In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malformed DNS data is present in PTR records. This is caused by a dn_expand oddity in octal printing.

Frequently asked questions

What is CVE-2026-40684?: In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malformed DNS data is present in PTR records. This is caused by a dn_expand oddity in octal printing.
How severe is CVE-2026-40684?: CVE-2026-40684 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-40684 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40684?: CVE-2026-40684 affects Exim. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-40684?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40684 have an EU (EUVD) identifier?: Yes. CVE-2026-40684 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-26442.
When was CVE-2026-40684 published?: CVE-2026-40684 was published on 2026-04-30 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

193.202.11.112 (ipv4-addr)
76.12.128.249 (ipv4-addr)
50.116.72.139 (ipv4-addr)
166.62.41.190 (ipv4-addr)
160.187.147.124 (ipv4-addr)
132.148.155.138 (ipv4-addr)
77.221.151.241 (ipv4-addr)
37.221.254.200 (ipv4-addr)