CVE-2026-63443

Coder, a platform for provisioning remote development environments via Terraform, contains a server-side request forgery / redirect-handling flaw (CWE-918, CWE-863) in agentConn.apiClient(), which follows HTTP redirects and accepts the host from the redirected URL when the target port matches the workspace agent HTTP API port. An authenticated attacker who runs a modified workspace agent and knows another online agent's UUID can derive the victim's tailnet address and redirect the victim's control-plane requests to the attacker-influenced path: 301/302/303 redirects can hijack read requests, while 307/308 redirects replay write and process-start requests. The redirected workspace agent file APIs then read or write files as the victim workspace user, and versions exposing the workspace agent process API can achieve command execution after a redirected file write, crossing workspace and tenant boundaries. All self-hosted Coder deployments on versions prior to the fixes are affected; exploitation requires an authenticated account able to run a modified agent, so it primarily threatens multi-tenant or loosely restricted Coder installations. No public proof of concept is known and the issue is not in the CISA KEV catalog, so exploitation status is none known.

What to do: Upgrade to Coder 2.29.19, 2.32.9, 2.33.10, or 2.34.4 (or later) depending on your release line. Until patched, restrict which users can create or modify workspaces and workspace agents, and monitor audit logs for control-plane requests being redirected to agent tailnet addresses or unexpected cross-workspace file reads/writes and process-API calls.