CVE-2026-48783: Postiz Auth Bypass Vulnerability

CVE-2026-48783 Overview

CVE-2026-48783 affects Postiz, an AI-powered social media scheduling tool. Versions prior to 2.21.8 expose an unauthenticated endpoint at /public/modify-subscription that accepts a signed token and applies subscription-enforcement side effects without verifying the token's intended purpose. The flaw maps to CWE-345: Insufficient Verification of Data Authenticity. Although the endpoint cannot change the persisted subscription tier, it triggers enforcement actions on the caller's own organization. These actions include toggling team-member enablement, disabling integrations that exceed plan limits, and resetting the scheduled-post cron when the asserted plan is the free tier. Postiz patched the issue in version 2.21.8.

Critical Impact
An attacker can invoke unauthenticated enforcement logic against their own organization, disabling integrations and team members, and resetting scheduled-post cron jobs.

Affected Products

Postiz versions prior to 2.21.8
Self-hosted deployments of postiz-app
Postiz instances exposing the /public/modify-subscription endpoint

Discovery Timeline

2026-06-17 - CVE-2026-48783 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-48783

Vulnerability Analysis

The vulnerability resides in the /public/modify-subscription endpoint exposed by Postiz before version 2.21.8. The endpoint accepts a signed token and reads subscription claims from it, then applies enforcement side effects against the organization identified in those claims. The handler validates the signature of the token but does not verify the token's intended audience or purpose. As a result, tokens issued for other internal flows can be replayed at this endpoint to drive enforcement logic.

The endpoint does not persist a new subscription tier. Instead, it executes the downstream effects of a tier change against the caller's organization. Those effects include adjusting team-member enablement state, disabling integrations that exceed the asserted plan limits, and resetting the scheduled-post cron when the asserted plan is the free tier. Impact is bound to the attacker's own tenant, so cross-tenant pivoting through this endpoint is not possible.

Root Cause

The root cause is missing verification of token purpose, classified under [CWE-345]. The endpoint trusts the signature alone and does not bind the token to a specific action or audience. Authentication is also absent on the public route, which lets any network client invoke the enforcement path.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker obtains or reuses a signed token whose claims reference their own organization. The attacker sends the token to /public/modify-subscription, and the server runs the enforcement side effects against that organization. Exploitation conditions are constrained, which is reflected in the high attack complexity in the CVSS vector.

No verified public exploit code is available. See the GitHub Security Advisory GHSA-v4wr-4j8g-4hfj for technical details.

Detection Methods for CVE-2026-48783

Indicators of Compromise

Requests to /public/modify-subscription from unauthenticated sources or unexpected IP ranges
Unexplained changes to team-member enablement state within an organization
Integrations being disabled without an administrator action in the audit trail
Scheduled-post cron jobs resetting to free-tier intervals on paid organizations

Detection Strategies

Review web server and application logs for HTTP requests to the /public/modify-subscription path prior to upgrading to 2.21.8
Correlate signed-token usage with the originating endpoint to identify tokens replayed at the public subscription route
Alert on configuration-state transitions for integrations and team membership that are not tied to an administrator session

Monitoring Recommendations

Enable verbose request logging on the Postiz API gateway, capturing method, path, source IP, and token identifier
Track audit events for integration disablement, team-member state changes, and cron schedule resets
Monitor for spikes in 200-status responses on /public/* routes after deployment of 2.21.8

How to Mitigate CVE-2026-48783

Immediate Actions Required

Upgrade Postiz to version 2.21.8 or later using the official v2.21.8 release
Audit organization integrations, team-member states, and cron schedules for unexpected changes
Restrict network access to Postiz administrative and public endpoints to trusted sources where feasible

Patch Information

The maintainers fixed the issue in Postiz 2.21.8. The fix is included in the upstream commit 23696d2, which enforces verification of the token's intended purpose before applying subscription-enforcement side effects. Refer to the Gadvisory Security Advisory PSA-2026-WWFR8X for additional context.

Workarounds

Block external access to /public/modify-subscription at a reverse proxy or web application firewall until the upgrade is applied
Rotate signing keys used for internal subscription tokens to invalidate any replayable tokens already in circulation
Review and tighten access control on all /public/* routes that accept signed tokens

bash

# Example NGINX rule to block the vulnerable endpoint until patched
location = /public/modify-subscription {
    return 403;
}