Overview
The CVE-2026-4505 vulnerability affects eosphoros-ai DB-GPT up to version 0.7.5 and relates to the FastAPI Endpoint component within the project. The issue centers on the function module_plugin.refresh_plugins in the file packages/dbgpt-serve/src/dbgpt_serve/agent/hub/controller.py, which allowed an attacker to perform unrestricted uploads by manipulating the target plugin resource without proper authorization. This is a textbook case of broken object-level authorization (CWE-284) paired with unrestricted upload (CWE-434). An attacker could remotely trigger the vulnerable path, upload arbitrary data or payloads, and potentially overwhelm or compromise the system, depending on what is accepted and stored. The public disclosure and lack of timely vendor response underscore the risk of unpatched deployments and the critical need for defensive remediations in similar FastAPI endpoints.
In FastAPI, object-level authorization failures manifest when a handler uses client-supplied identifiers (such as plugin_id) to operate on resources without verifying ownership or permissions. An endpoint that accepts a resource identifier and a file upload, then writes to a shared storage location based solely on that identifier, can enable attackers to affect resources belonging to other users. This is especially dangerous for plugin management or deployment workflows where uploaded artifacts may be trusted content executed by the application. Without explicit ownership checks, input validation, and strict access control, any user could modify or replace content they do not own, leading to data integrity issues, privilege escalation, or remote code execution paths in downstream components.
Remediation for this class of vulnerability involves robust object-level authorization, strict input validation, and safer handling of uploads within FastAPI. Key mitigations include enforcing authentication and authorization checks against a durable ownership model (e.g., a database mapping resource_id to owner_id), whitelisting allowed upload types and sizes, storing artifacts in per-user or per-resource sandboxes, and auditing access. Additionally, ensuring dependency-driven access control, comprehensive tests (including negative tests for unauthorized access), and upgrading to patched releases when available are essential. The CVE references CWE-284 and CWE-434 to emphasize the need for strict access controls around resource modification and file uploads in FastAPI services.
Affected Versions
0.7.5 and earlier (<= 0.7.5)
Code Fix Example
FastAPI API Security Remediation
## VULNERABLE
from fastapi import FastAPI, UploadFile, File, HTTPException, Depends
from fastapi.security import OAuth2PasswordBearer
import os
app_vuln = FastAPI()
oauth2_scheme = OAuth2PasswordBearer(tokenUrl='/token')
def get_current_user(token: str = Depends(oauth2_scheme)):
if not token:
raise HTTPException(status_code=401)
return {"id": "user123", "username": "demo"}
PLUGIN_OWNERS = {"pluginA": "user123", "pluginB": "user456"}
PLUGIN_DIR = "./plugins_vuln"
@app_vuln.post('/plugins/{plugin_id}/refresh')
async def refresh_plugins_vuln(plugin_id: str, file: UploadFile = File(...), current_user = Depends(get_current_user)):
content = await file.read()
os.makedirs(PLUGIN_DIR, exist_ok=True)
target = os.path.join(PLUGIN_DIR, f"{plugin_id}.zip")
with open(target, 'wb') as f:
f.write(content)
return {"status": "uploaded", "path": target}
if __name__ == '__main__':
import uvicorn
uvicorn.run(app_vuln, host='0.0.0.0', port=8000)
## FIXED
from fastapi import FastAPI, UploadFile, File, HTTPException, Depends
from fastapi.security import OAuth2PasswordBearer
import os
app_fixed = FastAPI()
oauth2_scheme = OAuth2PasswordBearer(tokenUrl='/token')
def get_current_user(token: str = Depends(oauth2_scheme)):
if not token:
raise HTTPException(status_code=401)
return {"id": "user123", "username": "demo"}
PLUGIN_OWNERS = {"pluginA": "user123", "pluginB": "user456"}
PLUGIN_DIR = "./plugins_fixed"
MAX_SIZE = 5 * 1024 * 1024 # 5 MB
@app_fixed.post('/plugins/{plugin_id}/refresh')
async def refresh_plugins_fix(plugin_id: str, file: UploadFile = File(...), current_user = Depends(get_current_user)):
# Enforce ownership (object-level authorization)
if plugin_id not in PLUGIN_OWNERS:
raise HTTPException(status_code=404, detail="Plugin not found")
if PLUGIN_OWNERS[plugin_id] != current_user["id"]:
raise HTTPException(status_code=403, detail="Not authorized to modify this plugin")
# Validate upload
if not file.filename.endswith('.zip'):
raise HTTPException(status_code=400, detail='Invalid file type; .zip required')
contents = await file.read()
if len(contents) > MAX_SIZE:
raise HTTPException(status_code=413, detail='Uploaded file too large')
os.makedirs(PLUGIN_DIR, exist_ok=True)
target = os.path.join(PLUGIN_DIR, f"{plugin_id}.zip")
with open(target, 'wb') as f:
f.write(contents)
return {"status": "uploaded", "path": target}
if __name__ == '__main__':
import uvicorn
uvicorn.run(app_fixed, host='0.0.0.0', port=8001)