Server-Side Request Forgery in ChatGPTNextWeb Proxy Handler

A flaw has been found in ChatGPTNextWeb NextChat up to 2.16.1. This vulnerability affects the function proxyHandler of the file app/api/proxy.ts of the component Proxy Fallback Handler. This manipulation of the argument x-base-url causes server-side request forgery. It is possible to initiate the attack remotely. The exploit has been published and may be used. The pull request to fix this issue awaits acceptance.

Casky was already ahead

This CVE exploits attack patterns that Casky's 331matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

ChatGPTNextWeb (NextChat) versions up to 2.16.1 contain a critical server-side request forgery (SSRF) vulnerability in the proxy fallback handler component. The flaw exists in the proxyHandler function within app/api/proxy.ts, where insufficient validation of the x-base-url argument allows attackers to manipulate server requests to arbitrary destinations. This vulnerability is particularly concerning because it affects a widely-used web interface for AI interactions, potentially exposing internal network resources, cloud metadata endpoints, and backend services to unauthorized access. Any organization running vulnerable versions of NextChat—whether as a self-hosted deployment or integrated service—faces immediate risk of information disclosure and lateral movement attacks.

Casky.ai's 331 mapped skills detect this vulnerability pattern across MITRE ATT&CK techniques TA0001 (Initial Access) and TA0006 (Credential Access). Practitioners using Casky would identify suspicious activity through detection of unusual x-base-url parameter values combined with outbound requests to unexpected internal IP ranges (10.x.x.x, 172.16.x.x, 192.168.x.x) or cloud metadata services (169.254.169.254). Extended reasoning analysis would flag requests attempting to access local file:// schemes, internal service discovery patterns, or timing anomalies consistent with port scanning behavior. Security teams would see correlated findings showing reconnaissance attempts (TA0001: Resource Development) immediately followed by credential theft attempts against discovered internal services (TA0006), revealing the full attack chain rather than isolated events.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

331 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-105238.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0006

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