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TI-2026-39868 Aliases CVE-2026-55187GHSA-w4mc-hhc6-xp28

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

Priority HIGH 65CWE-918Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Information disclosure
Confidentiality · integrity · availability
Low · None · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-918 and the CVSS impact.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00354 29th percentileScored 2026-11-07
Fix Fixed mailpit (axllent): 1.30.2github.com/axllent/mailpit (Go): 1.30.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
axllentmailpitbefore 1.30.21.30.2Patch availableCNA
—github.com/axllent/mailpit (Go)before 1.30.21.30.2Patch availableGHSA-w4mc-hhc6-xp28
  • mailpit Vendoraxllent Affected before 1.30.2 Fixed in 1.30.2 Patch available CNA
  • github.com/axllent/mailpit (Go) Vendor— Affected before 1.30.2 Fixed in 1.30.2 Patch available GHSA-w4mc-hhc6-xp28

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:axllent:mailpit:*:*:*:*:*:*:*:*——axllent
  • cpe:2.3:a:axllent:mailpit:*:*:*:*:*:*:*:* Versions — — ·axllent

Remediation

  • Fix · CNA mailpit (axllent) Fixed in 1.30.2
  • Fix · GHSA-w4mc-hhc6-xp28 github.com/axllent/mailpit (Go) Fixed in 1.30.2 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-55187
  2. 2026-10-03 Alias added: GHSA-w4mc-hhc6-xp28

References

Advisory 1

Other 4

  • TI-2026-22161 Mailpit is Vulnerable to Server-Side Request Forgery (SSRF) via Link Check API CVSS 3.1HIGH 8.6
  • TI-2026-33452 Mailpit: Unauthenticated remote memory-exhaustion DoS via unlimited SMTP DATA and /api/v1/send body sizes CVSS 3.1HIGH 7.5
  • TI-2026-33450 Mailpit: Path traversal & arbitrary file write in mailpit dump --http via attacker-controlled message IDs CVSS 3.1HIGH 8.2
  • TI-2026-17561 Mailpit Proxy Endpoint is Vulnerable to Server-Side Request Forgery (SSRF) CVSS 3.1MEDIUM 5.8
  • TI-2026-47725 Mailpit: SMTP DATA line reader buffers over-limit input before size enforcement CVSS 3.1MEDIUM 5.3
  • TI-2026-47724 Mailpit: Thumbnail generation decodes unbounded image dimensions before scaling CVSS 3.1MEDIUM 5.3
See all 15 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences