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VulnerabilityPublished

CVE-2026-121880: Posit Workbench · Insecure Direct Object Reference

Affects Posit WorkbenchSource CVE Database V5

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Public exploit available · CVSS 4.7 Medium : upgrade to 2026.08.0 as a priority.

Data as of 6 Nov 2026, 15:34 UTC

CVSS 4.0 base score
4.7Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (POSIT)CVSS 4.04.7
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:Amber

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 6 Nov 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: evidence found.

    CVSS exploit maturity: proof of concept public

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

ProductAffectedFixed in
Posit Software, PBCPosit WorkbenchAffected
  • <2026.08.0
Fixed in
  • 2026.08.0
Posit Software, PBCRStudio ServerAffected
  • <2026.08.0
Fixed in
  • 2026.08.0

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.

References

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