CVE-2026-86183: Diem Project Authorization Bypass Vulnerability

CVE-2026-86183 Overview

CVE-2026-86183 is an authorization bypass vulnerability [CWE-285] in the Diem content management system (diem-project/diem) versions up to 5.1.3. The flaw resides in the dmFrontPlugin/modules/dmWidget/lib/BasedmWidgetActions.class.php file within the dmWidget component. Attackers can manipulate the widget_id argument to bypass authorization checks and interact with widgets they should not be able to access. The vulnerability is remotely exploitable and requires no authentication or user interaction. A public exploit exists, and the maintainers were notified through an issue report but have not responded.

Critical Impact

Remote, unauthenticated attackers can bypass authorization controls in the dmWidget component by manipulating the widget_id parameter, resulting in unauthorized access to widget functionality.

Affected Products

• diem-project diem versions up to and including 5.1.3
• Deployments using the dmFrontPlugin module
• Web applications relying on the vulnerable BasedmWidgetActions.class.php file

Discovery Timeline

• 2026-09-06 - CVE-2026-86183 published to the National Vulnerability Database
• 2026-09-08 - Last updated in NVD database
• Patch identifier - Commit hash 116974edfb9a5b8bd69cb13586dc62bcdbb485ad referenced as the remediation

Technical Details for CVE-2026-86183

Vulnerability Analysis

The vulnerability affects widget-handling logic in the Diem CMS front-end plugin. The BasedmWidgetActions.class.php file processes the widget_id argument without enforcing sufficient authorization checks. An attacker sending a crafted request with a manipulated widget_id value can reach widget actions that should be restricted to authorized users. Because the flaw is reachable over the network without credentials, it can be leveraged directly against exposed Diem installations. The public availability of exploit information lowers the effort required to weaponize the issue against unpatched deployments.

Root Cause

The root cause is improper authorization [CWE-285] in the dmWidget action handler. The application accepts the widget_id parameter and performs widget operations without validating that the requesting user is entitled to act on the referenced widget. This design gap allows an attacker to reference arbitrary widget identifiers and bypass intended access controls.

Attack Vector

The attack vector is network-based with low complexity. An attacker crafts an HTTP request targeting the vulnerable widget action endpoint and supplies a widget_id value corresponding to a widget the attacker should not access. Because no authentication or user interaction is required, exploitation can be scripted and repeated at scale against internet-exposed Diem instances. Technical detail is available in the GitHub Issue #450 Discussion and the VulDB CVE-2026-86183 Details entry.

// No verified exploit code is published in the reference set.
// Refer to the linked VulDB and GitHub issue for parameter-level details.

Detection Methods for CVE-2026-86183

Indicators of Compromise

• HTTP requests to Diem front-end routes containing unexpected or enumerated widget_id parameter values
• Access patterns showing widget interactions from unauthenticated sessions or unusual source IP addresses
• Web server logs referencing dmWidget module endpoints outside of normal administrative workflows

Detection Strategies

• Inspect application and web server logs for widget_id parameter values that do not match legitimate front-end navigation
• Correlate widget-action requests with session state to identify calls made without an authenticated session
• Deploy web application firewall (WAF) rules that flag direct requests to dmWidget action handlers from external sources

Monitoring Recommendations

• Enable verbose request logging on the Diem front-end plugin routes and forward logs to a centralized analytics platform
• Alert on sequential enumeration of the widget_id parameter, which suggests scripted probing
• Monitor for anomalous outbound activity or configuration changes originating from the Diem web server following suspicious widget requests

How to Mitigate CVE-2026-86183

Immediate Actions Required

• Apply the upstream fix identified by commit 116974edfb9a5b8bd69cb13586dc62bcdbb485ad from the GitHub Diem Project Repository
• Restrict network access to Diem administrative and widget endpoints using firewall or reverse-proxy allowlists
• Audit web server logs for prior exploitation attempts against dmWidget routes

Patch Information

The maintainers have not published an official advisory, but the referenced patch commit 116974edfb9a5b8bd69cb13586dc62bcdbb485ad in the diem-project repository addresses the authorization gap. Organizations should build from the patched source or apply the diff to affected installations of Diem 5.1.3 or earlier. Track the GitHub Issue #450 Discussion for maintainer updates.

Workarounds

• Place the Diem application behind an authenticating reverse proxy to block unauthenticated requests to widget endpoints
• Add WAF rules that reject requests containing widget_id values inconsistent with expected front-end usage
• Temporarily disable the dmWidget front-end module if it is not required for site operation

# Example WAF rule (ModSecurity-style) to block direct external access to dmWidget actions
SecRule REQUEST_URI "@rx /dmWidget/" \
  "id:1026086183,phase:1,deny,status:403,\
   msg:'Block external access to Diem dmWidget endpoint (CVE-2026-86183)'"