CVE-2026-79673: Ech0 Authentication Bypass Vulnerability

CVE-2026-79673 Overview

CVE-2026-79673 is an authorization vulnerability in Ech0, a lightweight self-hosted microblogging application, affecting versions before 4.4.3. The PUT /user endpoint is gated by the profile:read scope, which by design should permit only read operations. The endpoint accepts write operations, including password changes, in violation of the declared scope contract. An attacker holding an administrator's profile:read access token can reset the admin password, authenticate with the new credentials, and receive an unrestricted session token. The resulting session bypasses all scope enforcement, converting a read-only token into full administrative control. The weakness is classified under CWE-863: Incorrect Authorization.

Critical Impact
A read-only access token can be escalated to a full administrator session, resulting in complete compromise of the Ech0 instance and all hosted content.

Affected Products

Ech0 versions prior to 4.4.3
Deployments exposing PUT /user with scoped access tokens
Ech0 instances issuing profile:read tokens to third-party integrations

Discovery Timeline

2026-08-25 - CVE-2026-79673 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-79673

Vulnerability Analysis

Ech0 implements OAuth-style scoped tokens to constrain what a bearer can do against the API. The profile:read scope communicates read-only intent, typically granted to integrations that display user profile data. The PUT /user route accepts this scope for authorization but does not restrict the operation type to reads.

As a result, a client presenting a profile:read token can submit a password change through the same endpoint. Once the password is rotated, the attacker performs a normal login and receives a full session token issued outside the scoped-token system. This session token is not filtered by scope checks, so every subsequent request executes with the user's full privileges. When the compromised token belongs to an administrator, the attacker inherits administrative control of the instance, including content management and user administration.

Root Cause

The root cause is a mismatch between the declared authorization policy and the enforced policy on PUT /user. Scope validation checks only that a recognized scope is present rather than confirming that the requested action is a read. Password updates should require an explicit write scope, such as profile:write or a dedicated credential-change scope, along with re-authentication.

Attack Vector

Exploitation requires an attacker to obtain a profile:read token belonging to a privileged account. The attacker issues an HTTP PUT request to /user containing a new password value, authenticated with the scoped bearer token. Ech0 accepts the request and updates the credential. The attacker then submits standard login credentials and receives an unrestricted session token, completing the privilege escalation.

No user interaction is required beyond the initial token exposure. See the GitHub Security Advisory GHSA-hm2h-wwwh-g49x and the VulnCheck advisory for additional technical detail.

Detection Methods for CVE-2026-79673

Indicators of Compromise

PUT /user requests authenticated with tokens carrying only the profile:read scope
Password change events for administrator accounts followed within seconds by a successful login from the same or nearby source IP
Unexpected issuance of full session tokens shortly after scoped-token API activity
Administrator sessions originating from IP addresses associated with third-party integrations that should only hold read scopes

Detection Strategies

Correlate access logs to flag any PUT, POST, or PATCH requests to /user where the presented token scope is profile:read.
Alert when a password change is followed by an authentication success for the same account within a short time window.
Baseline scope-to-endpoint mappings and alert on deviations where read scopes are used against write endpoints.

Monitoring Recommendations

Forward Ech0 application and reverse-proxy logs to a central analytics platform for scope and endpoint correlation.
Track administrative account credential changes and session token issuance as high-priority events.
Review OAuth token grants regularly to identify long-lived profile:read tokens issued to administrator accounts.

How to Mitigate CVE-2026-79673

Immediate Actions Required

Upgrade Ech0 to version 4.4.3 or later on all instances.
Revoke existing profile:read tokens, especially any issued to administrator accounts, and reissue with least-privilege scopes.
Reset administrator passwords and invalidate active sessions after upgrading.
Audit recent PUT /user activity for signs of unauthorized password changes.

Patch Information

The maintainer released Ech0 4.4.3, which corrects the scope enforcement on the PUT /user endpoint so that write operations, including password changes, are rejected when only profile:read is presented. Deployment details are documented in the GitHub Security Advisory.

Workarounds

Restrict access to PUT /user at the reverse proxy or web application firewall until the upgrade is applied.
Avoid issuing profile:read tokens to administrator accounts; use dedicated non-privileged accounts for read-only integrations.
Require re-authentication for any credential change flow enforced at a proxy layer where possible.

bash

# Example NGINX rule to block PUT/PATCH/POST on /user until patched
location = /user {
    limit_except GET {
        deny all;
    }
    proxy_pass http://ech0_backend;
}