CVE-2026-121880
Received
Received - Intake
Authorization Bypass in Posit Workbench via Port-Proxy
Vulnerability report for CVE-2026-121880, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-11-06
Last updated on: 2026-11-06
Assigner: 8c484e69-127d-402b-9cdb-5f86ef43eb86
Description
Description
Authorization bypass through user-controlled key in the localhost port-proxy (/p/<token>/) in Posit Software, PBC RStudio Server and Posit Workbench before 2026.08.0 allows remote authenticated users to reach web applications and other services bound to 127.0.0.1 under a different user's session, and to view their live rendered content and data, via a proxy URL constructed from the attacker's own port token for an arbitrary port number. The port token is a documented obfuscation measure and not an authorization boundary, and the proxy does not verify that the requested port belongs to the requesting user's session.
NOTE: exploitation requires an authenticated account on the same multi-user server and a target service listening on localhost at the time of access. Impact may be greater on hosts that co-locate additional privileged localhost services, and the bypass is not prevented by allow-shell=false; no setting restricts the port-proxy without disabling all application proxying.
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| Posit Software, PBC | Posit Workbench | From 0 (inc) to 2026.8.0 (exc) |
| Posit Software, PBC | RStudio Server | From 0 (inc) to 2026.8.0 (exc) |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-639 | The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. |
| CWE-862 | The product does not perform an authorization check when an actor attempts to access a resource or perform an action. |
