CVE-2026-85740
Deferred Deferred - Pending Action

IPv4-in-IPv6 Transition Bypass in LightRAG Parser

Publication date: 2026-09-22

Last updated on: 2026-09-22

Assigner: GitHub, Inc.

Description
LightRAG provides simple and fast retrieval-augmented generation. Prior to 1.5.5, _validated_addresses in lightrag/parser/markdown/parser.py evaluates the literal resolved address with ipaddress.is_global without consistently classifying an IPv4 address embedded in an IPv6 transition wrapper. A caller who can upload a Markdown or textpack document can supply an external image URL using NAT64 64:ff9b::/96 or an IPv4-compatible form that embeds a loopback, private, or cloud-metadata IPv4 address. On a deployment with compatible NAT64 or DNS64 routing, _download and _build_guarded_opener accept the wrapper and fetch the internal resource, whose body is then ingested. Current interpreter behavior already blocks some RFC 8215 and 6to4 forms, but the fixed guard handles all documented wrappers without becoming more permissive than the standard library. This issue is fixed in version 1.5.5.

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Meta Information

Published
2026-09-22
Last Modified
2026-09-22
Generated
2026-09-22
AI Q&A
2026-09-22
EPSS Evaluated
N/A
NVD
CVE-2026-85740
EUVD
EUVD-2026-84549

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
hkuds lightrag to 1.5.5 (exc)
lightrag lightrag 1.5.5

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-918 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.

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Executive Summary

CVE-2026-85740 is a Server-Side Request Forgery (SSRF) vulnerability in LightRAG's markdown parser affecting versions before 1.5.5. The issue occurs because the parser fails to properly validate IPv6-transition addresses like NAT64 or IPv4-compatible formats. These addresses can embed internal IPv4 addresses (e.g., loopback or private IPs) that bypass the global-routability check using Python's ipaddress.is_global. Attackers with upload privileges can exploit this to fetch sensitive internal resources.

Detection Guidance

To detect this SSRF vulnerability in LightRAG, monitor for unusual outbound requests to internal or private IP addresses from the application. Check logs for requests to cloud metadata endpoints (e.g., 169.254.169.254) or loopback addresses (e.g., 127.0.0.1). Use network monitoring tools like tcpdump or Wireshark to capture traffic from the LightRAG process. Inspect markdown or textpack files uploaded to the system for embedded IPv6-transition addresses (e.g., NAT64 64:ff9b::/96, 6to4 2002::/16).

Commands to check for vulnerable versions: grep -r "lightrag/parser/markdown/parser.py" /path/to/lightrag/ | grep "_validated_addresses". If the file exists and the function is present without the fix, the system is vulnerable.

Impact Analysis

An attacker could upload a malicious Markdown or textpack file with an embedded IPv6-transition address pointing to internal services like cloud metadata endpoints (e.g., 169.254.169.254), loopback addresses, or private networks. If the system uses NAT64/DNS64 routing, the parser would incorrectly allow the request, potentially exposing confidential data or internal resources to unauthorized access.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR's data protection principles or HIPAA's requirements for safeguarding protected health information. A breach exposing internal resources may result in non-compliance, legal penalties, or reputational damage due to unauthorized data exposure.

Mitigation Strategies

Immediately upgrade LightRAG to version 1.5.5 or later, which includes the fix for this SSRF vulnerability. If upgrading is not immediately possible, disable the markdown image-download feature or restrict upload permissions to trusted users only. Review and update SSRF protection rules to explicitly block IPv6-transition addresses (e.g., NAT64, 6to4) and internal IP ranges. Monitor network traffic for suspicious outbound requests to internal endpoints.

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