CVE-2026-123870: [Eclipse CSI - otterdog] Unauthenticated remote code execution via eval() on format-string-injected webhook body when GITHUB_WEBHOOK_SECRET is unset

The otterdog webapp evaluates a format-string built from the incoming GitHub webhook JSON body using Python's eval(). When the GITHUBWEBHOOKSECRET configuration value is unset or empty (the code default is None), the HMAC signature check is skipped entirely, allowing an unauthenticated network client to reach the eval() sink with attacker-controlled input and execute arbitrary Python on the webapp host.