# CVE-2026-82639: NextChat improper URL validation in proxy endpoint

Source: https://junglewise.ai/threats/cve-2026-82639-nextchat-improper-url-validation-in-proxy-endpoint  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-30. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-82639 · Severity: high · CVSS 7.5 · Published 2026-08-30

NextChat is an AI chat assistant application that supports multiple models including GPT and Claude. A vulnerability in versions 2.15.8 through 2.16.1 allows attackers to steal the server's OpenAI API key by crafting requests to a proxy endpoint. An attacker can exploit this to access the server's credentials and make unauthorized API calls at the victim's expense.

## Quick answers

**Is CVE-2026-82639 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-82639 being exploited in the wild.

**How severe is CVE-2026-82639?** High severity, with a CVSS score of 7.5, published 30 August 2026.

**Which products and versions are affected?** ChatGPTNextWeb NextChat 2.15.8 through 2.16.1.

**Is there a fix for CVE-2026-82639?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-82639 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-82639?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is an improper URL validation flaw in the proxy endpoint (app/api/proxy.ts). The code uses substring matching (`baseUrl?.includes("api.openai.com")`) to validate the x-base-url header instead of proper hostname parsing. This allows an attacker to bypass validation by sending any URL containing "api.openai.com" (e.g., "http://attacker.com/api.openai.com"), and the server will forward the OpenAI API key in the Authorization header to the attacker's server. The attack is network-accessible and requires no authentication or user interaction beyond crafting a specially-formed request. Patches are available in versions after 2.16.1.

## Affected products

- ChatGPTNextWeb NextChat 2.15.8 through 2.16.1

## Timeline

- 2026-08-30: disclosed

## References

- [https://github.com/ChatGPTNextWeb/NextChat](https://github.com/ChatGPTNextWeb/NextChat)
- [https://github.com/ChatGPTNextWeb/NextChat/blob/v2.16.1/app/api/proxy.ts](https://github.com/ChatGPTNextWeb/NextChat/blob/v2.16.1/app/api/proxy.ts)