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Back to active CVEs
Medium · CVSS 4.7CVE-2026-121880

RStudio Server / Posit Workbench localhost port-proxy does not enforce per-session port ownershipCVE-2026-121880

Answer in brief

CVE-2026-121880 records a Medium severity (CVSS 4.7) vulnerability in RStudio Server / Posit Workbench localhost port-proxy does not enforce per-session port ownership. The current sources do not mark it as known exploited. The current feed maps Posit Software, PBC/Posit Workbench (generic), Posit Software, PBC/RStudio Server (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Nov 6, 2026Updated Nov 6, 2026Source checked Nov 6, 2026First seen by HOL Nov 6, 2026Material review Nov 6, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 4.7
Exploitation
Not marked as known exploited
Affected software
2 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 4.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Posit Software, PBC/Posit Workbench (generic), Posit Software, PBC/RStudio Server (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
Posit Software, PBC/Posit Workbenchgeneric>=0 <2026.08.02026.08.0
Posit Software, PBC/RStudio Servergeneric>=0 <2026.08.02026.08.0

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for Posit Software, PBC/Posit Workbench, Posit Software, PBC/RStudio Server.
  2. 2Review the reported fix. Source-reported solution: Upgrade to Posit Workbench 2026.08.0 or later, or RStudio Server 2026.08.0 or later. The patched releases verify that a port requested through the localhost port-proxy belongs to the requesting user's session.

Evidence timeline and material changes

  1. Published upstream

    Nov 6, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Nov 6, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Nov 6, 2026

Sources and claim methodology

  • Source referencedocs.posit.co
  • Source referencetrust.posit.co
Upstream source 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.

Quoted source text, attributed separately from HOL analysis.

Related CVEs

  • Posit Workbench code-server session-state RPC (get_last_seen) SQL injectionSame posit software, pbc/posit workbench package
  • Ground Station 0.6.0 before 0.8.20 Credential Disclosure via get-orbital-sourcesAlso CWE-862
  • Grida through 0.0.24 Missing Authorization in Forms File-Preview APIAlso CWE-862
  • ChatWiki before 2.10.0 Cross-Tenant Fast Command Modification via saveFastCommandAlso CWE-639
  • xxyopen/201206030 novel Book Chapter Read BookServiceImpl.java getBookChapter authorizationAlso CWE-639
  • ChatWiki before 2.10.0 Cross-Tenant IDOR via SaveFormField and UpdateFormRequiredAlso CWE-639

Record context

Vulnerability class
Missing Auth
EPSS
Not reported
CWE IDs
CWE-639, CWE-862
Source
CVE List V5
Source checked
Nov 6, 2026
References
2 linked sources
Open source record