CVE-2026-53840: OpenClaw < 2026.5.12 - Custom Header Leakage via MCP Streamable HTTP Cross-Origin Redirects
Summary
OpenClaw supports remote MCP Streamable HTTP servers with operator-configured custom headers. In affected releases, those headers could be forwarded when the MCP endpoint responded with a cross-origin redirect.
This issue is limited to configured MCP Streamable HTTP servers that use custom headers. It does not expose unrelated OpenClaw credentials.
Affected configurations
This affects deployments where an MCP server is configured with:
- transportType: "streamable-http" - sensitive custom headers under mcp.servers..headers - an MCP endpoint that is malicious, compromised, or able to redirect to another origin
Impact
Custom MCP headers, such as API keys or tenant-routing headers, could be sent to the redirect target. The exposed credential scope depends on the header the operator configured for that MCP server.
Patched Versions
The first stable patched version is 2026.5.12.
Mitigations
Upgrade to openclaw@2026.5.8 or later. Before upgrading, avoid custom MCP headers with servers you do not fully trust, and rotate any MCP-specific credentials that may have been exposed by a redirecting endpoint.
Other sources
OpenClaw before 2026.5.12 contains an information disclosure vulnerability in streamable-http MCP servers that forwards operator-configured custom headers during cross-origin redirects. Attackers controlling or compromising an MCP endpoint can redirect requests to exfiltrate sensitive headers like API keys or tenant-routing credentials to attacker-controlled origins.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/openclawto a version that resolves this vulnerability.Fixed in 2026.5.12 - Upgrade
Upgrade
npm/openclawto a version that resolves this vulnerability.Fixed in 2026.5.8 - Configuration
Before upgrading, avoid configuring custom MCP headers with servers you do not fully trust; remove sensitive headers (for example API keys or tenant-routing headers) from mcp.servers.*.headers for such servers.
OpenClaw (MCP server configuration) mcp.servers.*.headers = avoid custom headers for untrusted MCP servers - Operational
Rotate any MCP-specific credentials that may have been exposed by a redirecting endpoint.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-53840?
The severity of CVE-2026-53840 is medium with a score of 6.
What does CVE-2026-53840 expose?
CVE-2026-53840 exposes custom headers from MCP Streamable HTTP servers via cross-origin redirects.
How can I fix CVE-2026-53840?
To fix CVE-2026-53840, upgrade to OpenClaw version 2026.5.12 or later.
Which versions of OpenClaw are affected by CVE-2026-53840?
OpenClaw versions prior to 2026.5.12 are vulnerable to CVE-2026-53840.
What type of attack does CVE-2026-53840 enable?
CVE-2026-53840 enables info leakage through custom headers exposed in cross-origin redirects.