What happened
VulnCheck published (2026-10-19) that LangBot through 4.11.0 fails to verify the Lark/Feishu webhook signature, allowing unauthenticated attackers to inject forged im.message.receive_v1 / card.action.trigger events. CVSS 6.5 (v3.1) / 8.3 (v4.0), CWE-345.
Why it matters
Chat-connector webhooks are a common entry point into agent workflows. Forging a legitimate-looking chat event lets an outsider drive an enterprise LangBot agent to run tools, trigger approvals, and answer as other users, bypassing the chat channel's authenticity boundary.
Attack vector
The Lark/Feishu webhook controller skips signature verification (CWE-345 missing authenticity verification). An attacker knowing a bot UUID POSTs fabricated events to the webhook endpoint, injecting messages into the LLM conversation pipeline and triggering tools and approval flows on behalf of legitimate users.
Affected systems
LangBot through 4.11.0
Mitigation
Update LangBot to a version incorporating the fix commit (43c481d74a6388657b84baa7d292c613c75c24f9).