diff --git a/cmd/rollcall/firmware.go b/cmd/rollcall/firmware.go
index 81c9db0..ee25ad9 100644
--- a/cmd/rollcall/firmware.go
+++ b/cmd/rollcall/firmware.go
@@ -469,6 +469,23 @@ func (a *App) runFirmware(jobID, machineID string, resume bool) {
 	_ = json.Unmarshal(j.Spec, &sp)
 	var pr fwProgress
 	_ = json.Unmarshal(j.Progress, &pr)
+	// every call reads the record again: the BMC certificate pin may change on the way
+	via := func(op, arg string) (string, error) {
+		if mm, err := a.store.Get(ctx, machineID); err == nil {
+			m = mm
+		}
+		out, err := a.firmwareVia(ctx, m, op, arg)
+		if err != nil && sp.Component == "bmc" && strings.Contains(err.Error(), "certificate changed") {
+			// the BMC we are updating came back with a new certificate: expected, pin it anew
+			_ = a.setBMCExtra(ctx, machineID, "tls_fingerprint", "")
+			_ = a.store.AddEvent(ctx, machineID, "bmc certificate", "changed during the BMC update; pinned again")
+			if mm, gerr := a.store.Get(ctx, machineID); gerr == nil {
+				m = mm
+			}
+			out, err = a.firmwareVia(ctx, m, op, arg)
+		}
+		return out, err
+	}
 	finish := func(state, msg string) {
 		_ = a.store.FinishJob(ctx, j.ID, state, map[bool]string{true: "", false: msg}[state == "done"])
 		ev := "firmware " + state
@@ -486,7 +503,7 @@ func (a *App) runFirmware(jobID, machineID string, resume bool) {
 			return
 		}
 		arg, _ := json.Marshal(fwStartArg{URL: a.firmwareURL(m, p), File: p.File, Component: p.Component, Method: sp.Method, Apply: sp.Apply})
-		out, err := a.firmwareVia(ctx, m, "fw-start", string(arg))
+		out, err := via("fw-start", string(arg))
 		if err != nil {
 			finish("failed", err.Error())
 			return
@@ -500,7 +517,7 @@ func (a *App) runFirmware(jobID, machineID string, resume bool) {
 	if pr.Task != "" && pr.Phase == "flashing" {
 		var lastOK time.Time = time.Now()
 		for {
-			out, err := a.firmwareVia(ctx, m, "fw-poll", pr.Task)
+			out, err := via("fw-poll", pr.Task)
 			if err != nil {
 				if time.Since(lastOK) > 25*time.Minute {
 					finish("failed", "the BMC has not answered for 25 minutes: "+err.Error())
@@ -517,7 +534,7 @@ func (a *App) runFirmware(jobID, machineID string, resume bool) {
 			pr.Pct, pr.Msg = pl.Pct, pl.Msg
 			a.setFWProgress(ctx, j, pr)
 			if pl.State == "failed" {
-				_, _ = a.firmwareVia(ctx, m, "fw-finish", "")
+				_, _ = via("fw-finish", "")
 				finish("failed", orDefault(pl.Msg, "the BMC reported the update failed"))
 				return
 			}
@@ -531,7 +548,7 @@ func (a *App) runFirmware(jobID, machineID string, resume bool) {
 			time.Sleep(15 * time.Second)
 		}
 	}
-	_, _ = a.firmwareVia(ctx, m, "fw-finish", "") // e.g. Lenovo's busy flag
+	_, _ = via("fw-finish", "") // e.g. Lenovo's busy flag
 	// a component that applies at the next reset (BIOS, most NICs/RAID) waits for it
 	if sp.Reboot && pr.Phase != "verifying" {
 		pr.Phase, pr.Msg = "rebooting", "power cycle so the update applies"
@@ -545,7 +562,15 @@ func (a *App) runFirmware(jobID, machineID string, resume bool) {
 	a.setFWProgress(ctx, j, pr)
 	deadline := time.Now().Add(20 * time.Minute) // servers take minutes to POST, BMCs to come back
 	for {
+		if mm, gerr := a.store.Get(ctx, machineID); gerr == nil {
+			m = mm
+		}
 		inv, err := a.readFirmware(ctx, m)
+		if err != nil && sp.Component == "bmc" && strings.Contains(err.Error(), "certificate changed") {
+			_ = a.setBMCExtra(ctx, machineID, "tls_fingerprint", "")
+			time.Sleep(5 * time.Second)
+			continue
+		}
 		if err == nil {
 			for _, c := range inv {
 				if c.Component == sp.Component && fwSameVersion(c.Version, sp.Version) {
diff --git a/cmd/rollcall/ipmi.go b/cmd/rollcall/ipmi.go
index 0f40c7d..2a25010 100644
--- a/cmd/rollcall/ipmi.go
+++ b/cmd/rollcall/ipmi.go
@@ -69,9 +69,66 @@ func (a *App) power(ctx context.Context, m *Machine, op, arg string) (string, er
 	if err != nil {
 		return "", fmt.Errorf("%w: %v", errNoBMC, err)
 	}
+	if c, err = a.pinBMC(ctx, m, c); err != nil {
+		return "", err
+	}
 	return a.powerVia(ctx, a.rackOf(m), c, op, arg)
 }
 
+// pinBMC records the certificate of an HTTPS BMC (Redfish, Proxmox) before
+// any credentials go to it: trust on first use. From then on every connection
+// must show the same certificate (bmcHTTPClient). An address change or a BMC
+// firmware update through Rollcall clears the pin; so does tls_fingerprint=.
+func (a *App) pinBMC(ctx context.Context, m *Machine, c *bmcCreds) (*bmcCreds, error) {
+	d, _ := driverByName(c.Driver)
+	if (d.Family != "redfish" && d.Family != "api") || c.Extra["tls_fingerprint"] != "" || c.Extra["verify_tls"] == "true" {
+		return c, nil
+	}
+	fp, err := a.powerVia(ctx, a.rackOf(m), c, "tls-fingerprint", "")
+	if err != nil {
+		if strings.Contains(err.Error(), "unknown power operation") { // a rack controller not updated yet
+			return c, nil
+		}
+		return nil, fmt.Errorf("reading the BMC's certificate: %w", err)
+	}
+	fp = strings.TrimSpace(fp)
+	if err := a.setBMCExtra(ctx, m.ID, "tls_fingerprint", fp); err != nil {
+		return nil, err
+	}
+	_ = a.store.AddEvent(ctx, m.ID, "bmc certificate pinned", fp)
+	c2 := *c
+	c2.Extra = map[string]string{}
+	for k, v := range c.Extra {
+		c2.Extra[k] = v
+	}
+	c2.Extra["tls_fingerprint"] = fp
+	return &c2, nil
+}
+
+// setBMCExtra sets (or with "" removes) one setting on a machine's BMC record.
+func (a *App) setBMCExtra(ctx context.Context, id, k, v string) error {
+	m, err := a.store.Get(ctx, id)
+	if err != nil || m.BMC == nil {
+		return err
+	}
+	var b obj
+	if err := json.Unmarshal(m.BMC, &b); err != nil {
+		return err
+	}
+	ex, _ := b["extra"].(map[string]any)
+	if ex == nil {
+		ex = map[string]any{}
+	}
+	if v == "" {
+		delete(ex, k)
+	} else {
+		ex[k] = v
+	}
+	b["extra"] = ex
+	nb, _ := json.Marshal(b)
+	return a.store.SetBMC(ctx, id, nb, nil)
+}
+
 func (a *App) powerVia(ctx context.Context, rack string, c *bmcCreds, op, arg string) (string, error) {
 	if rack == a.cfg.RackName || rack == "" {
 		return powerRun(ctx, a.cfg.IPMITool, c, op, arg)
@@ -90,6 +147,9 @@ func (a *App) firmwareVia(ctx context.Context, m *Machine, op, arg string) (stri
 	if err != nil {
 		return "", fmt.Errorf("%w: %v", errNoBMC, err)
 	}
+	if c, err = a.pinBMC(ctx, m, c); err != nil {
+		return "", err
+	}
 	rack := a.rackOf(m)
 	if rack == a.cfg.RackName || rack == "" {
 		return powerRun(ctx, a.cfg.IPMITool, c, op, arg)
@@ -152,6 +212,12 @@ func (a *App) probeBMC(m *Machine) {
 	}
 	probe := *c
 	probe.Driver, probe.Port = "redfish", 0
+	pinned, err := a.pinBMC(context.Background(), m, &probe)
+	if err != nil {
+		_ = a.store.AddEvent(context.Background(), m.ID, "bmc probe", "staying on ipmi: "+oneLine(err.Error()))
+		return
+	}
+	probe = *pinned
 	ctx, cancel := context.WithTimeout(context.Background(), 90e9)
 	defer cancel()
 	out, err := a.powerVia(ctx, a.rackOf(m), &probe, "probe", "")
@@ -235,7 +301,12 @@ func (a *App) handleBMC(w http.ResponseWriter, r *http.Request) {
 		b["driver"] = *req.Driver
 	}
 	if req.Address != nil {
-		b["address"] = strings.TrimSpace(*req.Address)
+		if a := strings.TrimSpace(*req.Address); a != str(b["address"]) {
+			if ex, _ := b["extra"].(map[string]any); ex != nil {
+				delete(ex, "tls_fingerprint") // another BMC: its certificate is pinned anew
+			}
+			b["address"] = a
+		}
 	}
 	if req.Port != nil {
 		b["port"] = *req.Port
diff --git a/cmd/rollcall/power.go b/cmd/rollcall/power.go
index e911ef9..e5427b2 100644
--- a/cmd/rollcall/power.go
+++ b/cmd/rollcall/power.go
@@ -12,7 +12,11 @@ package main
 import (
 	"bytes"
 	"context"
+	"crypto/sha256"
+	"crypto/subtle"
 	"crypto/tls"
+	"crypto/x509"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -57,6 +61,11 @@ var errManualPower = errors.New("this machine has manual power control: do it by
 
 // powerRun executes one operation with a driver.
 func powerRun(ctx context.Context, ipmitool string, c *bmcCreds, op, arg string) (string, error) {
+	if op == "tls-fingerprint" {
+		ctx, cancel := context.WithTimeout(ctx, 20*time.Second)
+		defer cancel()
+		return bmcTLSFingerprint(ctx, c)
+	}
 	if t, ok := fwTimeouts[op]; ok { // firmware: Redfish UpdateService (redfish_fw.go)
 		ctx, cancel := context.WithTimeout(ctx, t)
 		defer cancel()
@@ -136,13 +145,69 @@ func ipmiExec(ctx context.Context, tool string, c *bmcCreds, args ...string) (st
 
 // ---------------------------------------------------------------- BMC HTTP (Redfish, Proxmox)
 
+// bmcHTTPClient: BMCs ship self-signed certificates, so a BMC is trusted by
+// the fingerprint of the certificate it showed first (extra tls_fingerprint,
+// pinned by the region before credentials are ever sent; see pinBMC).
+// verify_tls=true checks it against the system's CAs instead.
 func bmcHTTPClient(c *bmcCreds) *http.Client {
-	// BMCs ship self-signed certificates; checking them is opt-in (extra verify_tls=true)
-	tr := &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: c.Extra["verify_tls"] != "true"}, //nolint:gosec
-		DialContext: (&net.Dialer{Timeout: 10 * time.Second}).DialContext}
+	tc := &tls.Config{InsecureSkipVerify: c.Extra["verify_tls"] != "true"} //nolint:gosec // pinned below
+	if pin := strings.ToLower(c.Extra["tls_fingerprint"]); pin != "" && c.Extra["verify_tls"] != "true" {
+		tc.VerifyConnection = func(cs tls.ConnectionState) error {
+			if len(cs.PeerCertificates) == 0 {
+				return errors.New("the BMC sent no certificate")
+			}
+			got := certSHA256(cs.PeerCertificates[0])
+			if subtle.ConstantTimeCompare([]byte(got), []byte(pin)) != 1 {
+				return fmt.Errorf("the BMC's certificate changed (pinned %s, now %s): not sending credentials; if the BMC was replaced or got new firmware, clear tls_fingerprint to trust the new one", short(pin), short(got))
+			}
+			return nil
+		}
+	}
+	tr := &http.Transport{TLSClientConfig: tc, DialContext: (&net.Dialer{Timeout: 10 * time.Second}).DialContext}
 	return &http.Client{Timeout: 45 * time.Second, Transport: tr}
 }
 
+func certSHA256(c *x509.Certificate) string {
+	s := sha256.Sum256(c.Raw)
+	return hex.EncodeToString(s[:])
+}
+
+func short(fp string) string {
+	if len(fp) > 16 {
+		return fp[:16] + "…"
+	}
+	return fp
+}
+
+// bmcTLSFingerprint connects to the BMC's HTTPS port and returns its
+// certificate's SHA-256 (op tls-fingerprint): a handshake only, no request,
+// no credentials.
+func bmcTLSFingerprint(ctx context.Context, c *bmcCreds) (string, error) {
+	port := 443
+	if d, _ := driverByName(c.Driver); d.Family == "api" {
+		port = 8006
+	}
+	u, err := url.Parse(bmcBase(c, "https", port))
+	if err != nil {
+		return "", err
+	}
+	host := u.Host
+	if u.Port() == "" {
+		host = net.JoinHostPort(u.Hostname(), "443")
+	}
+	d := &tls.Dialer{NetDialer: &net.Dialer{Timeout: 10 * time.Second}, Config: &tls.Config{InsecureSkipVerify: true}} //nolint:gosec // reading the certificate is the point
+	conn, err := d.DialContext(ctx, "tcp", host)
+	if err != nil {
+		return "", err
+	}
+	defer conn.Close()
+	cs := conn.(*tls.Conn).ConnectionState()
+	if len(cs.PeerCertificates) == 0 {
+		return "", errors.New("the BMC sent no certificate")
+	}
+	return certSHA256(cs.PeerCertificates[0]), nil
+}
+
 // bmcBase builds https://host[:port] from the record; IPMI's port is not Redfish's.
 func bmcBase(c *bmcCreds, scheme string, defPort int) string {
 	a := strings.TrimRight(c.Address, "/")
diff --git a/cmd/rollcall/security_test.go b/cmd/rollcall/security_test.go
index 6c12c5e..40e09e4 100644
--- a/cmd/rollcall/security_test.go
+++ b/cmd/rollcall/security_test.go
@@ -1,12 +1,14 @@
 package main
 
 import (
+	"context"
 	"crypto/ecdsa"
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/json"
+	"net/http"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
@@ -142,3 +144,33 @@ func TestClientIP(t *testing.T) {
 		t.Errorf("through a rack: %s", ip)
 	}
 }
+
+// An HTTPS BMC is trusted by the certificate it showed first; another one
+// gets no credentials.
+func TestBMCCertificatePin(t *testing.T) {
+	seen := 0
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if _, _, ok := r.BasicAuth(); ok {
+			seen++
+		}
+		_, _ = w.Write([]byte(`{"PowerState":"On","Members":[{"@odata.id":"/redfish/v1/Systems/1"}]}`))
+	}))
+	defer srv.Close()
+	c := creds(srv.URL, "redfish")
+	fp, err := powerRun(context.Background(), "", c, "tls-fingerprint", "")
+	if err != nil || fp != certSHA256(srv.Certificate()) {
+		t.Fatalf("fingerprint %q %v", fp, err)
+	}
+	if seen != 0 {
+		t.Error("credentials were sent while reading the certificate")
+	}
+	c.Extra["tls_fingerprint"] = fp
+	if _, err := powerRun(context.Background(), "", c, "status", ""); err != nil {
+		t.Fatalf("pinned and matching: %v", err)
+	}
+	c.Extra["tls_fingerprint"] = strings.Repeat("ab", 32)
+	seen = 0
+	if _, err := powerRun(context.Background(), "", c, "status", ""); err == nil || !strings.Contains(err.Error(), "certificate changed") || seen != 0 {
+		t.Errorf("another certificate: %v (credentials sent %d times)", err, seen)
+	}
+}
diff --git a/lab/pve-vbmc/pve_redfish.py b/lab/pve-vbmc/pve_redfish.py
index f8ba453..7efcc9f 100644
--- a/lab/pve-vbmc/pve_redfish.py
+++ b/lab/pve-vbmc/pve_redfish.py
@@ -316,9 +316,15 @@ def make_handler(pve, prof, user, password, fw):
     return H
 
 
-def self_signed(addr):
-    d = tempfile.mkdtemp()
-    crt, key = os.path.join(d, "c.pem"), os.path.join(d, "k.pem")
+def self_signed(addr, vmid):
+    """A self-signed certificate, kept across restarts like a real BMC's (rm the files for a new one)."""
+    d = "/var/lib/pve-vbmc"
+    crt, key = os.path.join(d, f"tls-{vmid}.crt"), os.path.join(d, f"tls-{vmid}.key")
+    if os.path.exists(crt) and os.path.exists(key):
+        return crt, key
+    if not os.access(d, os.W_OK):
+        d = tempfile.mkdtemp()
+        crt, key = os.path.join(d, "c.pem"), os.path.join(d, "k.pem")
     subprocess.run(["openssl", "req", "-x509", "-newkey", "ec", "-pkeyopt", "ec_paramgen_curve:prime256v1", "-nodes", "-days", "3650",
                     "-subj", "/CN=pve-redfish", "-addext", f"subjectAltName=IP:{addr}", "-keyout", key, "-out", crt],
                    check=True, capture_output=True)
@@ -348,7 +354,7 @@ def main():
     ip = ipaddress.ip_address(addr)
     cls = Server6 if ip.version == 6 else ThreadingHTTPServer
     srv = cls((addr, int(entry.get("redfish_port", 443))), handler)
-    crt, key = self_signed(addr)
+    crt, key = self_signed(addr, args.vmid)
     ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
     ctx.load_cert_chain(crt, key)
     srv.socket = ctx.wrap_socket(srv.socket, server_side=True)