CVE-2026-82833: Doccano Auth Bypass Vulnerability

CVE-2026-82833 Overview

CVE-2026-82833 is an improper access control vulnerability [CWE-266] in Doccano, an open source annotation tool for machine learning practitioners that includes an Auto Labeling Pipeline Module for automated document annotation. The flaw affects versions up to 1.8.5 and resides in the ExampleDetail function exposed through the /v1/projects/1/examples/ endpoint of the Project Example Detail component. Authenticated remote attackers can manipulate this endpoint to bypass access controls and interact with example data outside their permission scope. Public exploit information exists, and the vendor did not respond to disclosure attempts.

Critical Impact
Authenticated remote attackers can bypass access controls on the Doccano Project Example Detail Endpoint, exposing labeled datasets to unauthorized viewing or modification.

Affected Products

Doccano Open Source Annotation Tools for Machine Learning Practitioners up to version 1.8.5
Doccano Auto Labeling Pipeline Module up to version 1.8.5
Doccano Project Example Detail Endpoint component (/v1/projects/1/examples/)

Discovery Timeline

2026-08-31 - CVE-2026-82833 published to NVD
2026-09-01 - Last updated in NVD database

Technical Details for CVE-2026-82833

Vulnerability Analysis

The vulnerability lives in the ExampleDetail handler that serves the /v1/projects/1/examples/ route in Doccano. This endpoint returns and modifies annotation examples tied to a project. According to the advisory, manipulation of the request against this handler leads to improper access controls, meaning authorization checks fail to bind the caller's role and project membership to the requested resource.

Doccano stores labeled documents, spans, and classification decisions that make up training data for downstream machine learning models. Weak access enforcement on the example detail endpoint permits users who possess valid credentials but lack authorization for a given project to read or modify annotations belonging to other projects.

The issue is remotely reachable over the network and requires low privileges. No user interaction is needed. VulDB tracks the flaw as publicly disclosed with exploit material available.

Root Cause

The root cause is missing or incorrect authorization logic in the ExampleDetail view of Doccano's REST API. The endpoint validates that a caller is authenticated but does not consistently verify that the authenticated caller is a member of the target project with the appropriate role. This maps to [CWE-266] Incorrect Privilege Assignment, where a lower-privileged principal effectively operates with the privileges of a project collaborator.

Attack Vector

An attacker registers or reuses a low-privilege Doccano account, obtains a session or token, and issues HTTP requests to /v1/projects/{id}/examples/ for project identifiers they do not own. Because the handler does not enforce project-scoped authorization, the server returns example data or accepts modifications. The attack is fully remote and requires only network reachability to the Doccano web service.

No verified proof-of-concept code is published in a public exploit database. Technical detail is referenced in the VulDB CVE-2026-82833 entry and associated VulDB Vulnerability #397245 record.

Detection Methods for CVE-2026-82833

Indicators of Compromise

Repeated authenticated HTTP requests to /v1/projects/{id}/examples/ where the requesting user is not listed as a project member in the Doccano database.
Access logs showing a single account enumerating sequential project IDs against the examples endpoint.
Unexpected modifications to annotation examples with updated_by fields referencing accounts outside the project roster.

Detection Strategies

Correlate Doccano application logs with the project membership table to identify cross-project access on /v1/projects/*/examples/ routes.
Deploy a reverse proxy or WAF rule that logs the authenticated user identifier alongside every request to example endpoints for later review.
Alert on anomalous request rates from a single Doccano account against the example detail API.

Monitoring Recommendations

Forward Doccano web server access logs and Django application logs to a centralized logging tier for retention and query.
Baseline normal per-user access to project endpoints and flag deviations, particularly enumeration patterns across projects/{id}.
Review audit trails for annotation changes on sensitive datasets used to train production ML models.

How to Mitigate CVE-2026-82833

Immediate Actions Required

Restrict network exposure of Doccano instances to trusted internal networks or VPN-reachable segments while a fix is unavailable.
Audit existing Doccano user accounts and remove or disable accounts that do not require access to sensitive projects.
Review project membership rosters and confirm that no unauthorized users appear as project contributors.

Patch Information

No vendor patch has been published for CVE-2026-82833. VulDB reports that the maintainers were contacted early during disclosure but did not respond. Operators should monitor the Doccano project repository for a fixed release above 1.8.5 and apply it once available.

Workarounds

Place Doccano behind an authenticating reverse proxy that enforces per-project authorization at the gateway based on group membership.
Segment Doccano deployments so that each sensitive dataset resides in a dedicated instance with an isolated user pool.
Disable self-service account registration on public-facing Doccano deployments to reduce the pool of authenticated attackers.

bash

# Example nginx snippet to restrict the vulnerable endpoint to an allowlisted network
location ~ ^/v1/projects/[0-9]+/examples/ {
    allow 10.0.0.0/8;
    deny all;
    proxy_pass http://doccano_backend;
}