CVE-2026-121880: Posit Workbench · Insecure Direct Object Reference
Affects Posit WorkbenchSource CVE Database V5
Public exploit available · CVSS 4.7 Medium : upgrade to 2026.08.0 as a priority.
Data as of 6 Nov 2026, 15:34 UTC
Thin evidence
One scorer or none| CNA (POSIT) | CVSS 4.0 | 4.7 |
|---|
- Patch
- Available – fixed in 2026.08.0
CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P/AU:Y/R:A/V:D/RE:M/U:AmberExploitation evidence
Disclosed: evidence found.
CVE published 6 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CVSS vector, the Metasploit, Exploit-DB and nuclei-templates index as of 6 Nov 2026.
What to do
Upgrade Posit Workbench and RStudio Server to 2026.08.0.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Posit Software, PBCPosit Workbench | Affected
| Fixed in
|
| Posit Software, PBCRStudio Server | Affected
| Fixed in
|
CPE configurations (2)
cpe:2.3:a:posit:workbench:*:*:*:*:*:*:*:*cpe:2.3:a:posit:rstudio_server:*:*:*:*:*:*:*:*
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.