Coder workspace agent restricted host redirect validation flaw

Vulnerability Key Information Summary Vulnerability Overview Type: HTTP redirection to a restricted host, causing the workspace agent's API client to follow the redirect and access an unintended agent address. Root Cause: follows redirects by default, and the restricted host list failed to validate the redirect target. This allowed requests to be redirected to unintended agent addresses, potentially leading to cross-agent access or information disclosure. Scope of Impact Affected Components: HTTP client logic related to in the repository. Affected Versions: branch (fixed in commit ). Affected Scenarios: When the workspace agent's API client initiates a request, if the server returns a redirect, the client follows it to an address outside the restricted host list, potentially accessing an unintended agent. Fix Solution Fix Commit: (commit hash as seen at the top of the page). Fix Details: 1. In , restricted the redirection behavior of to ensure that redirects are only allowed to addresses within the restricted host list. 2. In , added validation for and to ensure requests are only sent to the expected agent address. 3. In , added test cases to verify that the redirect behavior matches expectations. POC/Exploit Code ```go // Test case: Verify redirect behavior func TestAgentCombinations(t testing.T) { t.Parallel() cases := []struct { name string status int invoke func(ctx context.Context, workspaceAgentCom) error }{ { name: "get 302", status: http.StatusFound, invoke: func(ctx context.Context, workspaceAgentCom) error { _, err := com.ListenHTTPPorts(ctx) return err }, }, { name: "post 307", status: http.StatusTemporaryRedirect, invoke: func(ctx context.Context, workspaceAgentCom) error { return com.WriteFile(ctx, "/tmp/tailnet", strings.NewReader("redirect-body")) }, }, { name: "post 308", status: http.StatusPermanentRedirect, invoke: func(ctx context.Context, workspaceAgentCom) error { return com.WriteFile(ctx, "/tmp/tailnet", strings.NewReader("redirect-body")) }, }, } for _, tc := range cases { t.Run(tc.name, func(t testing.T) { t.Parallel() ctx := testutil.Context(t, testutil.WaitMedium) clientID := uuid.New() attackerID := uuid.New() clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t, derpPkg, attackerID, "attacker") clientCom, _ := newTailnetCom(t, derpPkg, clientID, "client") attackerCom, _ := newTailnetCom(t

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Coder workspace agent restricted host redirect validation flaw

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