How severe is CVE-2026-21859?

CVE-2026-21859 has a CVSS 3.x base score of 5.8, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2026-21859 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (51st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21859?

CVE-2026-21859 affects Axllent Mailpit. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-21859?

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

Does CVE-2026-21859 have an EU (EUVD) identifier?

Yes. CVE-2026-21859 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-1038.

When was CVE-2026-21859 published?

CVE-2026-21859 was published on 2026-01-08 and last updated on 2026-06-17.

CVE-2026-21859

CVE-2026-21859 is a medium-severity vulnerability in Axllent Mailpit with a CVSS 3.x base score of 5.8. 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-918.

Key facts

Severity: Medium (CVSS 3.x base score 5.8)
EPSS exploit prediction: 1% (51st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-1038
Weakness: CWE-918
Affected product: Axllent Mailpit
Published: 2026-01-08
Last modified: 2026-06-17

Description

Mailpit is an email testing tool and API for developers. Versions 1.28.0 and below have a Server-Side Request Forgery (SSRF) vulnerability in the /proxy endpoint, allowing attackers to make requests to internal network resources. The /proxy endpoint validates http:// and https:// schemes, but it does not block internal IP addresses, enabling attackers to access internal services and APIs. This vulnerability is limited to HTTP GET requests with minimal headers. The issue is fixed in version 1.28.1.

Frequently asked questions

What is CVE-2026-21859?: Mailpit is an email testing tool and API for developers. Versions 1.28.0 and below have a Server-Side Request Forgery (SSRF) vulnerability in the /proxy endpoint, allowing attackers to make requests to internal network resources. The /proxy endpoint validates http:// and https:// schemes, but it does not block internal IP addresses, enabling attackers to access internal services and APIs. This vulnerability is limited to HTTP GET requests with minimal headers. The issue is fixed in version 1.28.1.
How severe is CVE-2026-21859?: CVE-2026-21859 has a CVSS 3.x base score of 5.8, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2026-21859 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (51st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21859?: CVE-2026-21859 affects Axllent Mailpit. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-21859?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-21859 have an EU (EUVD) identifier?: Yes. CVE-2026-21859 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-1038.
When was CVE-2026-21859 published?: CVE-2026-21859 was published on 2026-01-08 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:axllent:mailpit:*:*:*:*:*:*:*:*

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