Mailpit
CVE-2026-21859
MEDIUM
GHSA-8v65-47jx-7mfr
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V4 - API and Web Service URL allowlisting, SSRF prevention
MITRE ATT&CK
2 techniques across 2 tactics: Initial Access, Credential Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS 5.8 (MEDIUM). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: None. Exploitable via remote/network. Public exploit/POC available. |
| Exploit ScenarioDerived | A remote attacker could exploit this vulnerability to compromise the affected system. |
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Alert meAnalysisAIv1 – Mar 12, 2026
Mailpit versions 1.28.0 and earlier contain a server-side request forgery vulnerability in the /proxy endpoint that permits unauthenticated attackers to probe and access internal network resources and services. The endpoint insufficiently validates destination addresses, allowing requests to internal IP ranges despite scheme validation. Public exploit code exists for this vulnerability, which is resolved in version 1.28.1.
Earlier versions of this analysis (1)
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. [CVSS 5.8 MEDIUM]
RemediationAI
A vendor patch is available — apply it immediately. Fixed in version 1.28.1.. Restrict network access to the affected service where possible.
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in go
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Classified as CWE-918 (Server-Side Request Forgery (SSRF)). Affects Mailpit. 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.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
Lifecycle Timeline
3DescriptionGitHub Advisory
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.
Executive ViewAI
Organizations using Mailpit should be aware of moderate risk from CVE-2026-21859, a server-side request forgery vulnerability rated CVSS 5.8. Users could be tricked into performing unintended actions. Proof-of-concept code is publicly available. A patch is available and should be applied during regular vulnerability management.
Apply vendor patch. If patching is delayed: implement egress filtering, block metadata endpoints.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Server-Side Request Forgery exploits applications that fetch remote resources based on user-supplied URLs.
Affected Products (CPE)GitHub Advisory
Mailpit versions up to 1.28.2 contains a vulnerability that allows attackers to intercept sensitive data such as email c
Mailpit versions prior to 1.29.2 contain a Server-Side Request Forgery vulnerability in the Link Check API that allows u
Mailpit versions before 1.28.3 contain a server-side request forgery vulnerability in the HTML Check feature that allows
Header injection in Mailpit's SMTP server prior to version 1.28.3 allows unauthenticated remote attackers to inject or m
Cross-site WebSocket hijacking in Mailpit 1.29.0-1.30.5 exposes live email metadata to any website the developer visits,
Memory exhaustion in Mailpit's SMTP server (versions 1.30.0 through 1.30.4) allows unauthenticated remote SMTP clients t
Exploit-DB