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TI-2026-85967 Aliases CVE-2026-121880GHSA-45mx-vf84-77ww

Authorization bypass in RStudio Server and Posit Workbench port proxy

Priority LOW 21CWE-639Published · Updated

Key facts

Attack vector
Local
Privileges required
Low
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
Security bypass
Confidentiality · integrity · availability
High · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-639.

Summary

RStudio Server and Posit Workbench before 2026.08.0 let a remote authenticated user reach web applications and other services bound to 127.0.0.1 under a different user's session, and view their live rendered content and data. The localhost port-proxy does not verify that the requested port belongs to the requesting user's session, and its port token is only an obfuscation measure (CWE-639). Exploitation requires an account on the same multi-user server and a target service listening on localhost.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00252 16th percentileScored 2026-11-07
Fix Fixed Posit Workbench (Posit Software, PBC): 2026.08.0RStudio Server (Posit Software, PBC): 2026.08.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
Posit Software, PBCPosit Workbenchbefore 2026.08.02026.08.0Patch availableCNA
Posit Software, PBCRStudio Serverbefore 2026.08.02026.08.0Patch availableCNA
  • Posit Workbench VendorPosit Software, PBC Affected before 2026.08.0 Fixed in 2026.08.0 Patch available CNA
  • RStudio Server VendorPosit Software, PBC Affected before 2026.08.0 Fixed in 2026.08.0 Patch available CNA

CPE names CNA · 2

CPEVersionsRoleVendor
cpe:2.3:a:posit:workbench:*:*:*:*:*:*:*:*———
cpe:2.3:a:posit:rstudio_server:*:*:*:*:*:*:*:*———
  • cpe:2.3:a:posit:workbench:*:*:*:*:*:*:*:* Versions — — ·—
  • cpe:2.3:a:posit:rstudio_server:*:*:*:*:*:*:*:* Versions — — ·—

Remediation

Upgrade RStudio Server and Posit Workbench to version 2026.08.0, the fixed version for both products. The sources list no advisory identifiers for this fix.

Written with Claude Haiku 5.5 from the sources below · 2026-11-06

  • Fix · CNA Posit Workbench (Posit Software, PBC) Fixed in 2026.08.0
  • Fix · CNA RStudio Server (Posit Software, PBC) Fixed in 2026.08.0

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Advisory ·

    Posit Workbench — Posit Workbench release notes

    2 records Highest priority Priority LOW 2 LOW

    Other records, highest priority first

    • TI-2026-85968 SQL injection in Posit Workbench code-server session-state RPCPriority LOW 25
    Show all 2 records → Advisory →
  • Advisory ·

    Posit Workbench — trust.posit.co/updates

    2 records Highest priority Priority LOW 2 LOW

    Other records, highest priority first

    • TI-2026-85968 SQL injection in Posit Workbench code-server session-state RPCPriority LOW 25
    Show all 2 records → Advisory →

Timeline

  1. 2026-11-06 Threatist record created from CVE-2026-121880
  2. 2026-11-06 CISA SSVC decision points changed
  3. 2026-11-06 Alias added: GHSA-45mx-vf84-77ww

References

Advisory 2

  • TI-2026-85968 SQL injection in Posit Workbench code-server session-state RPC CVSS 4.0MEDIUM 5.7

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences