Cloudreve: SSRF guard bypass: checkIP does not decode IPv6-transition wrappers (NAT64, IPv4-compatible, 6to4) reaching internal and cloud-metadata addresses

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-79913: 0.40% estimated exploitation activity in the next 30 days; percentile 34.46 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Cloudreve's server-side request forgery guard ValidateExternalURL (pkg/request/ssrf.go) resolves a user-supplied URL host and rejects it when any resolved IP is a loopback, private, link-local, multicast, unspecified, CGNAT, or the cloud-metadata address. The classification is performed by checkIP, which uses Go's net.IP builtins (IsLoopback, IsPrivate, IsLinkLocalUnicast, ...) directly on the resolved address. These builtins inspect only the outer IPv6 address and do not decode IPv4-in-IPv6 transition wrappers. An attacker who controls a hostname's AAAA record (or, on a DNS64/NAT64 network, any hostname) can point the remote-download URL at a NAT64 well-known-prefix address (64:ff9b::a.b.c.d, RFC 6052), an IPv4-compatible address (::a.b.c.d, RFC 4291), or a 6to4 address (2002:AABB:CCDD::, RFC 3056) that wraps an internal IPv4. Go classifies these wrappers as ordinary global IPv6 addresses, so checkIP accepts them; the network then delivers the request to the embedded…

Published by the source

22 Sep 2026, 20:40 UTC

Last modified by the source

1 Oct 2026, 20:45 UTC

Source last checked

26 Oct 2026, 15:29 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jvh5-97xg-v99f

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6572

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jvh5-97xg-v99f

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# Patch Next advisory brief: CVE-2026-79913

Advisory: Cloudreve: SSRF guard bypass: checkIP does not decode IPv6-transition wrappers (NAT64, IPv4-compatible, 6to4) reaching internal and cloud-metadata addresses
IDs: CVE-2026-79913, GHSA-jvh5-97xg-v99f
Record: https://patchnext.com/advisories/cve-2026-79913 (revision 3, source checked 26 Oct 2026, 15:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/cloudreve/Cloudreve/v4 4.0.0-20260715072853-1c5cad6dec7e. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/cloudreve/Cloudreve/v3: affected every version
- Go github.com/cloudreve/Cloudreve: affected every version
- Go github.com/cloudreve/Cloudreve/v4: affected < 4.0.0-20260715072853-1c5cad6dec7e; fixed in 4.0.0-20260715072853-1c5cad6dec7e

## Suggested inspection (read-only)
- Go github.com/cloudreve/Cloudreve/v3: check the installed version with your package manager.
- Go github.com/cloudreve/Cloudreve: check the installed version with your package manager.
- Go github.com/cloudreve/Cloudreve/v4: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/cloudreve/Cloudreve/v3, github.com/cloudreve/Cloudreve, github.com/cloudreve/Cloudreve/v4.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GO-2026-6572 (OSV record GO-2026-6572 lists affected ranges: Go github.com/cloudreve/Cloudreve >=0; Go github.com/cloudreve/Cloudreve/v3 >=0; Go github.com/cloudreve/Cloudreve/v4 >=0 <4.0.0-20260715072853-1c5cad6dec7e (fixed))
- Verified: https://osv.dev/vulnerability/GHSA-jvh5-97xg-v99f (OSV record GHSA-jvh5-97xg-v99f lists affected ranges: Go github.com/cloudreve/Cloudreve/v4 >=0 <4.0.0-20260715072853-1c5cad6dec7e (fixed))
- Verified: https://github.com/advisories/GHSA-jvh5-97xg-v99f (GitHub-reviewed advisory GHSA-jvh5-97xg-v99f lists affected ranges: Go github.com/cloudreve/Cloudreve/v4 >=0 <4.0.0-20260715072853-1c5cad6dec7e)

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