CVE-2026-86041

Spoofed proxy headers bypass an ezBookkeeping MCP IP allowlist

ezBookkeeping · ezBookkeeping MCP and API-token IP allowlists

First documented disclosure · Review checkpoint

Summary

An untrusted caller can pass an origin restriction and make token-authorized actions appear to come from a trusted address.

Severity and exploitation evidence

Medium · 5.3/10 · CVSS 4.0. Severity source.

Exploitation not established: The researcher reproduced the allowlist bypass and false attribution in test requests. No malicious activity was established.

Exploitation evidence source

Technical severity is not a measure of observed attacks or of risk to your deployment. Attempts, demonstrations, and successful compromise retain the qualifications in the source.

How the weakness works

The router trusted a forwarded address without configuring trusted proxies. The MCP allowlist, transaction attribution and logs used the same spoofable client IP.

Conditions required

Network access to the affected service and a usable allowed address. Protected data actions still require the corresponding valid token.

Potential impact

The IP gate can be bypassed. Authorized transactions and access logs can carry false origin information. An attacker without a token does not thereby gain access to protected data.

Affected versions and configurations

0.10.0 through versions before 1.6.0.

Fix and mitigation status

1.6.0 limits header trust to configured proxies or the default trusted proxy ranges.

Practical next steps

Update, explicitly configure trusted proxy peers and require the ingress to overwrite untrusted forwarding headers. Review origin logs alongside token identities.

Operating lesson

Keep source restrictions, token authorization and audit attribution as separate checks.

Evidence and limits

The June 16 public proxy-header change predates the July 19 release and advisory. The November 4 CNA identifies both the MCP and API-token paths. Default trusted ranges include private networks and should be narrowed where needed.

Sources