CVE-2026-53708: ContextForge AI Gateway SSRF Vulnerability

CVE-2026-53708 Overview

CVE-2026-53708 is a Server-Side Request Forgery (SSRF) vulnerability in IBM ContextForge, an AI gateway, registry, and proxy that provides centralized discovery, guardrails, and management for Model Context Protocol (MCP), Agent-to-Agent (A2A), and REST/gRPC APIs. Versions prior to 1.0.3 contain a DNS rebinding flaw in the /admin/gateways/test endpoint that allows authenticated attackers to bypass SSRF protections. The vulnerability stems from a Time-of-Check to Time-of-Use (TOCTOU) condition [CWE-350] where the hostname is validated once and resolved again during the actual connection. Successful exploitation can expose cloud metadata credentials, internal APIs, and enable internal network reconnaissance.

Critical Impact
Authenticated attackers with gateways.read permission can leverage DNS rebinding to reach cloud metadata services, internal APIs, and probe internal network ports, potentially exposing cloud credentials.

Affected Products

IBM ContextForge (mcp-context-forge) versions prior to 1.0.3
Deployments with MCPGATEWAY_ADMIN_API_ENABLED enabled
Instances using database-backed roles with gateways.read permission

Discovery Timeline

2026-09-14 - CVE-2026-53708 published to NVD
2026-09-14 - Last updated in NVD database

Technical Details for CVE-2026-53708

Vulnerability Analysis

The vulnerability resides in the /admin/gateways/test call site within mcpgateway/admin.py. The endpoint invokes validate_gateway_test_url() in mcpgateway/common/validators.py to resolve the target hostname and reject private, loopback, link-local, and cloud-metadata addresses. However, the ResilientHttpClient subsequently resolves the original hostname a second time without binding to the previously validated IP address.

This two-step resolution creates a TOCTOU window that attackers exploit via DNS rebinding. The ssrf_blocked_networks and ssrf_dns_fail_closed controls only apply to the validation-time result, leaving the connection-time resolution unprotected. The endpoint sets allow_admin_bypass=False, meaning a bootstrap-only virtual platform-admin identity without a database role cannot trigger the flaw.

Root Cause

The root cause is an authentication logic weakness classified as [CWE-350] (Reliance on Reverse DNS Resolution for a Security-Critical Action). The application trusts the DNS resolution performed during validation but does not pin the validated IP address for the subsequent HTTP request, allowing the resolver to return a different address on the second lookup.

Attack Vector

An attacker with a database-backed role containing explicit gateways.read permission configures an attacker-controlled DNS server with a short Time-To-Live (TTL). During validation, the DNS server returns a public address that passes the allowlist check. When ResilientHttpClient re-resolves the hostname, the DNS server returns a private RFC 1918 address, loopback address, or a cloud metadata endpoint such as 169.254.169.254. The connection then reaches internal services, exposing cloud credentials, internal APIs, or enabling port scanning of the internal network.

text

# Patch excerpt from .env.example adding DNS timeout control
# GATEWAY_TEST_DNS_TIMEOUT: Timeout in seconds for DNS resolution during gateway test
# validation. Prevents slow/malicious DNS servers from stalling the handler.
# Default: 5.0 seconds (range: 0.1 to 30.0)
# GATEWAY_TEST_DNS_TIMEOUT=5.0
#
# NOTE: Private IPs (RFC 1918), loopback addresses (127.0.0.0/8), and link-local
# addresses (169.254.0.0/16) are ALWAYS blocked regardless of allowlist configuration.

Source: GitHub Commit fba11a9

Detection Methods for CVE-2026-53708

Indicators of Compromise

Outbound connections from ContextForge to RFC 1918 private ranges, 127.0.0.0/8, or 169.254.169.254 immediately after /admin/gateways/test requests
DNS query patterns with abnormally short TTLs targeting hostnames used in gateway test requests
Unexpected access attempts to cloud provider metadata endpoints (AWS IMDS, Azure IMDS, GCP metadata)
Anomalous authentication events for users with gateways.read role permissions

Detection Strategies

Correlate /admin/gateways/test HTTP requests with subsequent egress connections to internal or metadata addresses
Inspect DNS resolver logs for hosts returning both public and private addresses within short intervals
Alert on ContextForge process connections to link-local, loopback, or RFC 1918 destinations

Monitoring Recommendations

Log all invocations of /admin/gateways/test including source identity, target URL, and resolved IP addresses
Deploy egress filtering to block ContextForge network access to metadata IPs and internal management ranges
Monitor role assignments granting gateways.read permission for unauthorized changes

How to Mitigate CVE-2026-53708

Immediate Actions Required

Upgrade IBM ContextForge to version 1.0.3 or later where the DNS rebinding flaw is patched
Audit all database-backed roles and remove gateways.read permission from accounts that do not require it
Disable MCPGATEWAY_ADMIN_API_ENABLED on instances that do not need administrative gateway management

Patch Information

The fix is available in ContextForge version 1.0.3. The patch introduces a configurable GATEWAY_TEST_DNS_TIMEOUT (default 5.0 seconds) and enforces IP address binding between validation and connection phases. Review the GitHub Release v1.0.3 and the GitHub Security Advisory GHSA-9hgc-g3w5-67cm for full remediation details.

Workarounds

Restrict egress network access from ContextForge to a strict allowlist of external destinations
Block all outbound traffic to cloud metadata endpoints such as 169.254.169.254 at the host or network firewall
Configure GATEWAY_TEST_ALLOWED_HOSTS to a minimal list of trusted external hostnames
Isolate ContextForge deployments in network segments without access to internal management APIs

bash

# Upgrade ContextForge to the patched version
pip install --upgrade mcp-contextforge-gateway==1.0.3

# Restrict allowed test hosts in environment configuration
export GATEWAY_TEST_ALLOWED_HOSTS='["api.trusted-partner.com"]'
export GATEWAY_TEST_DNS_TIMEOUT=5.0

# Block cloud metadata egress at the host level (Linux iptables example)
iptables -A OUTPUT -d 169.254.169.254 -j DROP