CVE-2026-21859Public exploitNetwork attack vector

Internal data disclosure via unrestricted proxy requests

Published Jan 7, 2026 · Updated Jan 7, 2026

SSRF in Axllent Mailpit before 1.28.1 allows remote attackers to read internal HTTP resources through the /proxy endpoint. ProxyHandler accepts any HTTP or HTTPS URL and issues a server-side GET without blocking internal addresses or restricting the destination to message assets. The endpoint is unauthenticated unless UI/API basic authentication is configured; requests have minimal headers and can disclose internal service data or captured email.

CVSS severity5.8
Medium
EPSS probability0.83%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in Axllent Mailpit before 1.28.1 allows remote attackers to read internal HTTP resources through the /proxy endpoint. ProxyHandler accepts any HTTP or HTTPS URL and issues a server-side GET without blocking internal addresses or restricting the destination to message assets. The endpoint is unauthenticated unless UI/API basic authentication is configured; requests have minimal headers and can disclose internal service data or captured email.

The record

CVE
CVE-2026-21859
Published
Jan 7, 2026
Updated
Jan 7, 2026
Vendor
Axllent
Product
Mailpit
Classifications
CWE-918, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.28.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Axllent · Mailpitversion=< 1.28.1

Published CVSS scores

5.3NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.8GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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