CVE-2026-16076: AstrBot Authentication Bypass Vulnerability

CVE-2026-16076 Overview

CVE-2026-16076 is an authentication bypass vulnerability [CWE-287] affecting AstrBotDevs AstrBot versions up to 4.25.5. The flaw resides in the OpenApiRoute.chat_send function within astrbot/dashboard/routes/open_api.py, part of the API component. Attackers can manipulate the Username argument to bypass authentication through spoofing. The attack is exploitable remotely and requires low privileges. Public disclosure of the exploit technique increases the risk of opportunistic abuse. The vendor was contacted prior to public disclosure but did not respond.

Critical Impact
Remote attackers with low privileges can spoof usernames through the chat_send API route to bypass authentication controls in AstrBot deployments.

Affected Products

AstrBotDevs AstrBot versions up to and including 4.25.5
Component: API (astrbot/dashboard/routes/open_api.py)
Function: OpenApiRoute.chat_send

Discovery Timeline

2026-07-18 - CVE-2026-16076 published to NVD
2026-07-20 - Last updated in NVD database

Technical Details for CVE-2026-16076

Vulnerability Analysis

The vulnerability affects the chat_send endpoint of AstrBot's Open API. The OpenApiRoute.chat_send handler accepts a Username parameter from client requests without adequately validating that the caller is authorized to act as that user. An attacker can supply an arbitrary value for the Username argument and impersonate another account within the AstrBot instance.

The issue is classified under [CWE-287] Improper Authentication. Because the identity assertion is client-controlled, the server treats spoofed requests as legitimate, undermining the authentication boundary of the API. The attack is network-reachable and requires only low privileges to execute.

AstrBot is a chatbot framework that integrates with multiple messaging platforms. Successful exploitation lets an attacker send chat messages, invoke bot commands, or interact with plugins in the context of an impersonated user, resulting in limited impact to confidentiality, integrity, and availability.

Root Cause

The root cause is reliance on a client-supplied Username value as an authoritative identity claim. The chat_send handler does not bind the requesting session or API token to the asserted username, allowing the caller to specify any account name. Trusting untrusted input for identity attribution is a well-documented anti-pattern in authentication design.

Attack Vector

An authenticated attacker with low-level API access issues a crafted HTTP request to the chat_send endpoint and sets the Username field to a targeted account. The AstrBot dashboard route processes the request under the spoofed identity, executing chat operations without validating ownership of the claimed username. A public proof-of-concept has been published, referenced in the GitHub PoC Snippet and cataloged in VulDB CVE-2026-16076.

No verified exploitation code is reproduced here. Refer to the linked references for the technical proof-of-concept and additional context.

Detection Methods for CVE-2026-16076

Indicators of Compromise

HTTP requests to /api/chat_send or equivalent Open API routes containing unexpected or mismatched Username values that do not correspond to the authenticated session identity.
Chat messages or bot commands attributed to users who did not authenticate during the corresponding time window.
Anomalous API traffic from IP addresses that authenticate as one user but submit requests referencing multiple Username values.

Detection Strategies

Enable verbose logging on the AstrBot dashboard routes to capture request bodies and header context for chat_send calls.
Correlate the authenticated session or API token with the Username argument in each request and alert on mismatches.
Review audit logs for chat activity that has no corresponding authentication event for the claimed user.

Monitoring Recommendations

Deploy a reverse proxy or web application firewall (WAF) in front of AstrBot to log and inspect all requests to open_api.py routes.
Rate-limit and alert on high-volume requests to chat_send originating from a single API key across many distinct usernames.
Retain API access logs for at least 90 days to support retrospective identification of impersonation activity.

How to Mitigate CVE-2026-16076

Immediate Actions Required

Restrict network exposure of the AstrBot dashboard and Open API endpoints to trusted networks or via VPN until a patched release is available.
Rotate any AstrBot API tokens and administrative credentials issued to the affected instance.
Review historical logs for the chat_send endpoint to identify any prior abuse of the Username parameter.

Patch Information

At the time of publication, the vendor did not respond to disclosure and no official fixed version is listed in the NVD entry. Monitor the AstrBot project on GitHub for a release beyond 4.25.5 that validates the Username argument against the authenticated principal. Additional references are available at VulDB Vulnerability #379791.

Workarounds

Place AstrBot behind an authenticating reverse proxy that injects and enforces the caller's identity, ignoring client-supplied Username values.
Disable the Open API interface if it is not required, or block the chat_send route at the proxy or firewall layer.
Apply a local source patch to astrbot/dashboard/routes/open_api.py that derives the username from the authenticated session context instead of the request body.

bash

# Example: block external access to the Open API route at the reverse proxy
location /api/chat_send {
    allow 10.0.0.0/8;
    deny all;
    proxy_pass http://127.0.0.1:6185;
}