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CVE-2026-21859— Mailpit Proxy Endpoint is Vulnerable to Server-Side Request Forgery (SSRF)

Quick assessment

Affected
axllent mailpit
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mailpit是Ralph Slooten个人开发者的一个电子邮件测试工具。 Mailpit 1.28.0及之前版本存在代码问题漏洞，该漏洞源于/proxy端点存在服务端请求伪造，允许攻击者访问内部网络资源。

CVSS 5.8 · Medium EPSS 0.81% · P56

Public Exploits 1

Nuclei · 1 CVE-2026-21859.yaml [template]

Possible ATT&CK Techniques 1 AI

T1598.001 · Spearphishing Service
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I. Basic Information for CVE-2026-21859

Vulnerability Information
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Vulnerability Title
Mailpit Proxy Endpoint is Vulnerable to Server-Side Request Forgery (SSRF)
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5
Vulnerability Title
Mailpit 代码问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mailpit是Ralph Slooten个人开发者的一个电子邮件测试工具。 Mailpit 1.28.0及之前版本存在代码问题漏洞，该漏洞源于/proxy端点存在服务端请求伪造，允许攻击者访问内部网络资源。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
axllent mailpit < 1.28.1 -

II. Public POCs for CVE-2026-21859

# POC Description Source Link Shenlong Link
1 Mailpit <= 1.28.0 contains a server-side request forgery caused by insufficient validation of internal IP addresses in the /proxy endpoint, letting attackers make requests to internal network resources, exploit requires crafted HTTP GET requests. https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-21859.yaml POC Details
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III. Intelligence Information for CVE-2026-21859

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Patches & Fixes for CVE-2026-21859 (1)

Vendor Advisories for CVE-2026-21859 (1)

IV. Related Vulnerabilities

Same product: mailpit
Same vendor: axllent
Same weakness: CWE-918

V. Comments for CVE-2026-21859

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