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Sync-in Server: SSRF protection bypass via IPv4-mapped IPv6 addresses in regExpPrivateIP

High severity GitHub Reviewed Published May 22, 2026 in Sync-in/server • Updated Jun 5, 2026

Package

npm @sync-in/server (npm)

Affected versions

<= 2.2.1

Patched versions

2.3.0

Description

Summary:
The private IP blocklist regex used in the URL download feature does not match IPv4-mapped IPv6 addresses (e.g. ::ffff:127.0.0.1), allowing SSRF protection to be bypassed on dual-stack systems.

Affected components

backend/src/applications/files/services/files-manager.service.ts – downloadFromUrl() checks regExpPrivateIP against request.socket.remoteAddress.
backend/src/applications/files/utils/url-file.ts – regExpPrivateIP does not include ::ffff: variants.

Details:
The regExpPrivateIP regex in backend/src/applications/files/utils/url-file.ts correctly blocks standard IPv4 private ranges but does not include ::ffff: prefixed variants. On dual-stack systems, Node.js can report a socket's remoteAddress in IPv4-mapped IPv6 form, meaning the check in FilesManager.downloadFromUrl() can be bypassed entirely.

PoC:
poc.pdf

Proof:
1000226655

Impact:
An attacker can supply a crafted URL pointing to an internal address that gets reported as ::ffff:127.0.0.1 or ::ffff:10.x.x.x, causing the server to fetch internal resources that should be blocked. Any user with access to the file download feature is a potential attacker.

References

@johaven johaven published to Sync-in/server May 22, 2026
Published to the GitHub Advisory Database Jun 5, 2026
Reviewed Jun 5, 2026
Last updated Jun 5, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(9th percentile)

Weaknesses

Server-Side Request Forgery (SSRF)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Learn more on MITRE.

CVE ID

CVE-2026-47684

GHSA ID

GHSA-q4x5-8cj6-52wg

Source code

Credits

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