GHSA-87qc-fj39-wccr Glances: XML-RPC Multi-Origin CORS Configuration Silently Falls Back to Wildcard (Incomplete Fix for CVE-2026-33533)
SummaryThe Glances XML-RPC server (`glances -s`) introduced a configurable CORS origin list in version 4.5.3 as a mitigation for CVE 2026-33533.  However, the implementation silently falls back to `Access-Control-Allow-Origin: *` whenever `cors_origins` contains more than one entry.  An operator who configures an explicit two-entry allowlist (e.g. two internal dashboard origins) intending to restrict browser access instead receives the unrestricted wildcard — the same exposure that the original CVE described.  A malicious web page served from any origin can issue a CORS simple request to `/RPC2` and read the full system monitoring dataset without the victim's knowledge.Details**Affected file:** `glances/server.py`, class `GlancesXMLRPCServer`, line 113**Direct URL (commit 04579778e733d705898a169e049dc84772c852da):**https://github.com/nicolargo/glances/blob/04579778e733d705898a169e049dc84772c852da/glances/server.py#L113The `cors_origin` value is then echoed back as the `Access-Control-Allow-Origin` response header for every request (line ~147 in the same file):This means the CORS header is determined once at server startup and never compared against the actual `Origin` header sent by the browser.  Even if an operator sets:the server responds with `Access-Control-Allow-Origin: *` to every request, including those from `https://attacker.example.com`.**Single-origin wildcard** (the default, `cors_origins = *`) is also still in effect; the fix only helps if exactly one non-wildcard origin is configured.**Confirmed on:** x86_64 Linux, Python 3.13, Glances 4.5.5_dev1 (commit 04579778e733d705898a169e049dc84772c852da).Test results:| Origin sent              | ACAO header returned | Expected     |
|--------------------------|----------------------|--------------|
| `http://evil.example.com`| `*`                  | No header    |
| `https://dashboard.corp` | `*`                  | Reflected    |
| `https://grafana.corp`   | `*`                  | Reflected    |PoC**Special configuration required**The multi-origin collapse is only triggered when `cors_origins` contains two or more entries.  Create the following `glances.conf`:**Step 1 — Start the XML-RPC server using the config above****Step 2 — Send a CORS simple request from a foreign origin****Expected (secure) response:**or no `Access-Control-Allow-Origin` header.**Actual response:****Step 3 — Demonstrate the code-level collapse to wildcard****Browser-based exploitation**Once the wildcard is confirmed, the original CVE-2026-33533 attack vector still applies in full.  A malicious page served to a victim whose browser can reach the Glances server can exfiltrate data as follows:This works as a CORS "simple request" (POST + `text/plain`) — no CORS preflight is triggered and the `*` wildcard allows the browser to read the response.Impact**Vulnerability type:** CORS Misconfiguration / Bypass of CVE-2026-33533 mitigation (CWE-942)**Who is impacted:** Any operator who:Runs Glances in XML-RPC server mode (`glances -s`), *and*Has configured two or more `cors_origins` entries in `glances.conf` believing
they are restricting browser access.Operators using the default single-wildcard configuration (`cors_origins = *`, which is the upstream default) remain affected by the original CVE-2026-33533 exposure (unrestricted cross-origin read).  The incomplete fix addresses only the narrow case of a single non-wildcard origin.**Data exposed through the XML-RPC API** includes: hostname, OS and kernel version, full process list with command-line arguments (frequently containing API keys, passwords, and tokens), CPU/memory/disk/network statistics, listening ports, and Docker/Kubernetes container metadata.**Impact:****Confidentiality:** High — complete system monitoring data readable by any browser page.**Integrity:** None — read-only API.**Availability:** None — no denial-of-service component.Suggested FixImplement per-request origin reflection against the configured allowlist, as recommended by the W3C CORS specification and as done by modern CORS middleware (e.g. Starlette's `CORSMiddleware`):Additionally, consider retiring the legacy XML-RPC server in favour of the REST API (`glances -w`), which uses Starlette's `CORSMiddleware` correctly, and document the deprecation path.Responsible DisclosureThe AFINE Team is committed to responsible / coordinated disclosure. The AFINE Team will not publish details of this vulnerability or release exploit code publicly until a fix has been released, or 90 days have elapsed from the date of this report, whichever comes first.CreditsThis issue was identified by Michał Majchrowicz and Marcin Wyczechowski, members of the AFINE Team.
CVSS v3.1 score: 7.4