CVE-2026-121880Posit Workbench insecure direct object reference
CVE-2026-121880 is a insecure direct object reference in Posit Workbench, rated medium (4.7 on CVSS 4.0).
Why this priority: Medium severity, with no exploitation signal.
Published · Updated · NVD status: Awaiting Analysis
What it is
Changing an identifier in a request reaches another user's records. An action never checks whether the caller is allowed to perform it.
How it is reached
An attacker can exploit it by someone who can already run code or sign in on the machine, with an ordinary user account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.
What an attacker gains
A successful attack can read the data it protects. In practice, this kind of flaw lets an attacker reach data or actions their role should not allow.
Is it being exploited?
There is no public report of exploitation yet.
What to do
- Upgrade Posit Workbench to 2026.08.0 or later. Other affected products have their own fixed versions on this page.
- Limit who can run code or sign in on the hosts that run it.
Description from NVD
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.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Permission checks in APIs and admin surfaces. The flaw sits between one role or tenant and another.
- Multi-tenant services. The flaw sits between one role or tenant and another.
Trust boundaries in play
- Host boundary. The attacker needs a foothold on the machine first; the flaw turns a small foothold into a bigger one.
- Between one role or tenant and another. An attacker who crosses it can reach data or actions their role should not allow.
Questions to answer about your own systems
- Where does Posit Workbench run in your systems, and at which version?
- Which of those hosts also run code or users you do not fully trust?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.