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CVE-2026-55187— Mailpit: Incomplete SSRF protection in Link Check API via IPv6 transition mechanisms (follow-up to CVE-2026-27808)

Quick assessment

Affected
axllent mailpit
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

axllent mailpit是axllent个人开发者开源的一款邮件测试与调试工具。 axllent mailpit 1.30.2之前版本存在服务端请求伪造漏洞，该漏洞源于tools.IsInternalIP拒绝列表依赖Go标准库分类辅助工具，未能阻止IPv6转换机制或前缀如NAT64、6to4、IPv4兼容IPv6、ISATAP、fec0::/10和2001:db8::/32，可能导致攻击者利用Link Check API的safeDialContext路径拨打内部目标，并通过状态码和错误反馈映射内部

CVSS 5.8 · Medium EPSS 0.38% · P31

Affected Version Matrix 1

VendorProduct Version RangeStatus
axllent mailpit < 1.30.2 affected
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I. Basic Information for CVE-2026-55187

Vulnerability Information
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Vulnerability Title
Mailpit: Incomplete SSRF protection in Link Check API via IPv6 transition mechanisms (follow-up to CVE-2026-27808)
Source: CVE Program / CVE List V5
Vulnerability Description
Mailpit is an email testing tool and API for developers. Prior to 1.30.2, the remediation shipped for CVE-2026-27808 is incomplete because the tools.IsInternalIP deny-list in internal/tools/net.go relies on Go's standard library classification helpers and does not block IPv6 transition mechanisms or prefixes such as NAT64, 6to4, IPv4-compatible IPv6, ISATAP, fec0::/10, and 2001:db8::/32. An attacker who can deliver email and invoke POST /api/v1/message/{ID}/link-check can coerce the Link Check API's safeDialContext path into dialing internal destinations and can use status-code and error feedback to map internal service reachability, including cloud metadata endpoints. This issue is fixed in version 1.30.2.
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
axllent mailpit 服务端请求伪造漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
axllent mailpit是axllent个人开发者开源的一款邮件测试与调试工具。 axllent mailpit 1.30.2之前版本存在服务端请求伪造漏洞，该漏洞源于tools.IsInternalIP拒绝列表依赖Go标准库分类辅助工具，未能阻止IPv6转换机制或前缀如NAT64、6to4、IPv4兼容IPv6、ISATAP、fec0::/10和2001:db8::/32，可能导致攻击者利用Link Check API的safeDialContext路径拨打内部目标，并通过状态码和错误反馈映射内部
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 < 1.30.2 -

II. Public POCs for CVE-2026-55187

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III. Intelligence Information for CVE-2026-55187

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Patches & Fixes for CVE-2026-55187 (1)

Vendor Advisories for CVE-2026-55187 (1)

Vendor Pages for CVE-2026-55187 (1)

IV. Related Vulnerabilities

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

V. Comments for CVE-2026-55187

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