CVE-2026-42883: Audiobookshelf Information Disclosure Flaw

CVE-2026-42883 Overview

CVE-2026-42883 is a broken access control vulnerability [CWE-863] in Audiobookshelf, a self-hosted audiobook and podcast server. The flaw exists in the GET /api/libraries/:id/download endpoint in versions prior to 2.32.2. The endpoint validates that the requesting user can access the library named in the URL path but fetches downloadable items using attacker-supplied item IDs without confirming those items belong to the validated library. An authenticated user with download permission on any single library can exfiltrate the full file contents of items in any other library, including libraries that explicitly deny that user access. The maintainer fixed the issue in version 2.32.2.

Critical Impact
Authenticated users with access to one Audiobookshelf library can download files from restricted libraries, breaking tenant isolation and exposing protected media content.

Affected Products

Audiobookshelf versions prior to 2.32.2
GET /api/libraries/:id/download API endpoint
Multi-user Audiobookshelf deployments using per-library access controls

Discovery Timeline

2026-05-11 - CVE-2026-42883 published to NVD
2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-42883

Vulnerability Analysis

The vulnerability is a classic Insecure Direct Object Reference (IDOR) caused by incomplete authorization logic. Audiobookshelf supports multi-user deployments where administrators grant per-library access permissions. The GET /api/libraries/:id/download route is intended to let an authorized user bundle and download files from a specific library. The handler checks whether the caller has access to the library identified by the :id path parameter, then fetches items using IDs supplied as query or body parameters. It never re-validates that those item IDs actually belong to the library named in the path.

An authenticated attacker with download rights to any single library can enumerate or guess item IDs and request them through a library :id they legitimately access. The server returns the file contents regardless of the item's true parent library. The attack requires only low privileges and no user interaction, and it is exploitable over the network against any exposed Audiobookshelf instance.

Root Cause

The root cause is missing object-to-container authorization. The endpoint authorizes the library context but does not enforce that requested item IDs are scoped to that library. Authorization decisions [CWE-863] are made on the wrong identifier, allowing trusted input from the URL path to mask untrusted input in the item IDs.

Attack Vector

Exploitation is performed over HTTPS by any authenticated account holding download permission on at least one library. The attacker issues a request to /api/libraries/{accessible_library_id}/download while specifying item IDs from a restricted library. The server returns the raw file contents. Refer to the GitHub Security Advisory GHSA-6rvg-w3f5-9gq5 for the official advisory.

Detection Methods for CVE-2026-42883

Indicators of Compromise

Requests to /api/libraries/:id/download containing item IDs that do not belong to the library specified in the URL path.
Single user accounts downloading abnormally large volumes of content or accessing many distinct item IDs in short windows.
Successful downloads logged for users whose user record explicitly excludes the source library.

Detection Strategies

Parse Audiobookshelf access logs and correlate the :id path parameter with the parent library of each returned item to surface mismatches.
Baseline normal per-user download rates and alert on deviations that suggest enumeration of item IDs.
Hunt for repeated 200 responses on /api/libraries/*/download from accounts that historically only access a narrow library scope.

Monitoring Recommendations

Forward Audiobookshelf application and reverse proxy logs to a centralized analytics platform such as Singularity Data Lake for OCSF-normalized querying and retention.
Enable verbose API logging on the Audiobookshelf instance to capture both the library path parameter and the requested item IDs.
Monitor outbound bandwidth from the Audiobookshelf host for spikes consistent with bulk media exfiltration.

How to Mitigate CVE-2026-42883

Immediate Actions Required

Upgrade all Audiobookshelf instances to version 2.32.2 or later without delay.
Audit existing user accounts and revoke download permission from accounts that do not require it.
Review historical access logs for cross-library download patterns that may indicate prior exploitation.

Patch Information

The vulnerability is fixed in Audiobookshelf 2.32.2. The patch constrains the items returned by GET /api/libraries/:id/download to those that actually belong to the library specified in the URL path. See the GitHub Security Advisory GHSA-6rvg-w3f5-9gq5 for release details.

Workarounds

Restrict network exposure of Audiobookshelf to trusted users via VPN or authenticated reverse proxy until the upgrade is applied.
Temporarily remove download permission from non-administrative accounts to reduce the population of users able to invoke the vulnerable endpoint.
Block requests to /api/libraries/*/download at the reverse proxy if the service cannot be patched immediately.

bash

# Upgrade Audiobookshelf via Docker to the patched release
docker pull ghcr.io/advplyr/audiobookshelf:2.32.2
docker stop audiobookshelf
docker rm audiobookshelf
docker run -d --name audiobookshelf \
  -p 13378:80 \
  -v /path/to/config:/config \
  -v /path/to/metadata:/metadata \
  -v /path/to/audiobooks:/audiobooks \
  ghcr.io/advplyr/audiobookshelf:2.32.2