diff --git a/CHANGELOG.md b/CHANGELOG.md
index 45b831d..30984aa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Security
+- [#87] Rotate the superuser password once in `post-upgrade.sh` — it may have been generated by a `doguctl` older than v0.12.2 which used `math/rand` instead of `crypto/rand`
+- [#87] Affected values are indistinguishable from safe ones, so every instance rotates regardless of its installed version, guarded by the new dogu config marker `password_rotated`
+- [#87] A fresh installation sets the marker in `initAdmin` and never rotates
 
 ## [v14.23-1] - 2026-06-23
 ### Changed
diff --git a/batsTests/post-upgrade.bats b/batsTests/post-upgrade.bats
index 5f48409..3542ba3 100755
--- a/batsTests/post-upgrade.bats
+++ b/batsTests/post-upgrade.bats
@@ -11,10 +11,13 @@ load '/workspace/target/bats_libs/bats-file/load.bash'
 
 setup() {
   doguctl="$(mock_create)"
+  psql="$(mock_create)"
   export doguctl
+  export psql
   export PATH="${BATS_TMPDIR}:${PATH}"
 
   ln -sf "${doguctl}" "${BATS_TMPDIR}/doguctl"
+  ln -sf "${psql}" "${BATS_TMPDIR}/psql"
 
   # Mocks für Systembefehle
   echo "#!/bin/bash" > "${BATS_TMPDIR}/chown"
@@ -117,4 +120,96 @@ load_script_safely() {
 
   assert_success
   assert_line "Postgresql post-upgrade done"
-}
\ No newline at end of file
+}
+
+
+@test "rotateSuperuserPassword guard suppresses rotation via rotation flag" {
+  # arrange
+  load_script_safely
+  mock_set_output "${doguctl}" "true"
+
+  # act
+  run rotateSuperuserPassword
+
+  # assert
+  assert_success
+  assert_equal "$(mock_get_call_num "${doguctl}")" "1"
+  assert_line "Superuser password has already been rotated; skipping"
+}
+
+@test "rotateSuperuserPassword() should rotate superuser password if not rotated before" {
+  # arrange doguctl
+  load_script_safely
+  mock_set_output "${doguctl}" "false" 1
+  mock_set_output "${doguctl}" "testusername" 2
+  mock_set_output "${doguctl}" "random123" 3
+
+  # arrange psql
+  local psql_mock_call_args
+  psql_mock_call_args="--variable=ON_ERROR_STOP=1"
+  psql_mock_call_args+=" --username=testusername"
+  psql_mock_call_args+=" --command=ALTER USER \"testusername\" WITH PASSWORD 'random123';"
+  
+  # act
+  run rotateSuperuserPassword
+
+  # assert
+  assert_success
+  assert_equal "$(mock_get_call_args "${doguctl}" 1)" "config --default false password_rotated"
+  assert_line "Rotating superuser password..."
+  assert_equal "$(mock_get_call_args "${doguctl}" 2)" "config --default postgres user"
+  assert_equal "$(mock_get_call_args "${doguctl}" 3)" "random"
+  assert_equal "$(mock_get_call_args "${doguctl}" 4)" "config --encrypted password random123"
+  assert_equal "$(mock_get_call_args "${psql}" 1)" "${psql_mock_call_args}"
+  assert_equal "$(mock_get_call_args "${doguctl}" 5)" "config password_rotated true"
+  assert_line "Superuser password rotated"
+
+  assert_equal "$(mock_get_call_num "${doguctl}")" "5"
+  assert_equal "$(mock_get_call_num "${psql}")" "1"
+}
+
+@test "rotateSuperuserPassword() should not set the flag if the database update fails" {
+  # arrange
+  load_script_safely
+  mock_set_output "${doguctl}" "false" 1
+  mock_set_output "${doguctl}" "testusername" 2
+  mock_set_output "${doguctl}" "random123" 3
+  mock_set_status "${psql}" 1 1 # psql fails
+
+  # act
+  # run seems to disable errexit so the psql failure would be ingored and flag "password_rotated" set true
+  # Another subshell with errexit validates cancelation.
+  run bash -c "source '${BATS_TMPDIR}/post-upgrade-patched.sh'; set -o errexit; rotateSuperuserPassword"
+
+  # assert
+  assert_failure
+  assert_line "Rotating superuser password..."
+  assert_equal "$(mock_get_call_args "${doguctl}" 4)" "config --encrypted password random123"
+  assert_equal "$(mock_get_call_num "${psql}")" "1"
+
+  # password is set in config, flag "password_rotated" is NOT.
+  # Only four doguctl calls.
+  assert_equal "$(mock_get_call_num "${doguctl}")" "4"
+  refute_line "Superuser password rotated"
+}
+
+@test "rotateSuperuserPassword() should not touch the database if writing the config fails" {
+  # arrange
+  load_script_safely
+  mock_set_output "${doguctl}" "false" 1
+  mock_set_output "${doguctl}" "testusername" 2
+  mock_set_output "${doguctl}" "random123" 3
+  # the fourth call is the one writing the new password into the config
+  mock_set_status "${doguctl}" 1 4
+
+  # act
+  run bash -c "source '${BATS_TMPDIR}/post-upgrade-patched.sh'; set -o errexit; rotateSuperuserPassword"
+
+  # assert
+  assert_failure
+  assert_line "Rotating superuser password..."
+  # If password could not be saved to config, "ALTER ... PASSWORD" should not be called
+  assert_equal "$(mock_get_call_num "${psql}")" "0"
+  assert_equal "$(mock_get_call_num "${doguctl}")" "4"
+  refute_line "Superuser password rotated"
+}
diff --git a/batsTests/startup.bats b/batsTests/startup.bats
index 735d520..29f667d 100644
--- a/batsTests/startup.bats
+++ b/batsTests/startup.bats
@@ -70,3 +70,18 @@ Ziel            Router          Genmask         Flags   MSS Fenster irtt Iface
   assert_line '# container networks'
   assert_line "host    all             all             192.168.179.0/24          password"
 }
+
+@test "initAdmin() should set flag password_rotated true" {
+  # arrange
+  source /workspace/resources/startup.sh
+  mock_set_output "${doguctl}" "GEHEIM123" 2
+
+  # act
+  run initAdmin
+
+  # assert
+  assert_success
+  assert_equal "$(mock_get_call_args "${doguctl}" 3)" "config -e password GEHEIM123"
+  assert_equal "$(mock_get_call_args "${doguctl}" 4)" "config password_rotated true"
+  assert_equal "$(mock_get_call_num "${doguctl}")" "4"
+}
\ No newline at end of file
diff --git a/docs/development/upgrade_dogu_de.md b/docs/development/upgrade_dogu_de.md
index 03647a7..6062eb5 100644
--- a/docs/development/upgrade_dogu_de.md
+++ b/docs/development/upgrade_dogu_de.md
@@ -33,12 +33,23 @@ Restore-Fall:
 Regulärer Migrationsfall:
 
 1. Wenn kein Restore nötig ist und eine DB bereits initialisiert ist, startet `post-upgrade.sh` PostgreSQL temporär.
-2. Danach werden Migrationsskripte aus `/docker-entrypoint-initdb.d` (aus `resources/migrations`) manuell ausgeführt.
-3. PostgreSQL wird wieder gestoppt und `local_state` entfernt.
+2. Das Superuser-Passwort wird einmalig rotiert (siehe unten).
+3. Danach werden Migrationsskripte aus `/docker-entrypoint-initdb.d` (aus `resources/migrations`) manuell ausgeführt.
+4. PostgreSQL wird wieder gestoppt und `local_state` entfernt.
+
+### Rotation des Superuser-Passworts (`rotateSuperuserPassword`)
+
+Vor `doguctl` v0.12.2 nutzte `doguctl random` Gos `math/rand` statt `crypto/rand`. Betroffene Werte sind nicht erkennbar, deshalb rotiert jede Instanz ohne Marker.
+
+1. Marker `password_rotated` in der Dogu-Config, kein Versionsvergleich.
+2. Reihenfolge: Config, dann `ALTER USER`, dann Marker — eine abgebrochene Rotation wird wiederholt.
+3. Läuft nach `startPostgresql`, weil `ALTER USER` eine laufende DB braucht. Über den Unix-Socket genügt `trust`, das alte Passwort wird nicht gebraucht.
+4. Im Restore-Fall nicht erreicht - dort setzt `initAdmin` Passwort und Marker.
 
 ### Startup (`resources/startup.sh`)
 
 `startup.sh` wartet, solange `local_state=upgrading` gesetzt ist.
+Bei leerem `PGDATA` (postgresql nicht installiert) setzt `initAdmin` zusätzlich `password_rotated=true`, da ein frisch erzeugtes Passwort sicher ist.
 Danach startet es `/usr/local/bin/docker-entrypoint.sh` mit den Dogu-spezifischen Parametern.
 
 Wichtig:
diff --git a/docs/development/upgrade_dogu_en.md b/docs/development/upgrade_dogu_en.md
index ec5924c..c9a6428 100644
--- a/docs/development/upgrade_dogu_en.md
+++ b/docs/development/upgrade_dogu_en.md
@@ -33,12 +33,23 @@ Restore case:
 Regular migration case:
 
 1. If no restore is needed and a DB is already initialized, `post-upgrade.sh` starts PostgreSQL temporarily.
-2. Then migration scripts from `/docker-entrypoint-initdb.d` (from `resources/migrations`) are executed manually.
-3. PostgreSQL is stopped again and `local_state` is removed.
+2. The superuser password is rotated once (see below).
+3. Then migration scripts from `/docker-entrypoint-initdb.d` (from `resources/migrations`) are executed manually.
+4. PostgreSQL is stopped again and `local_state` is removed.
+
+### Rotation of the superuser password (`rotateSuperuserPassword`)
+
+Before `doguctl` v0.12.2, `doguctl random` used Go's `math/rand` instead of `crypto/rand`. Affected values cannot be told apart from safe ones, so every instance without the marker rotates.
+
+1. Marker `password_rotated` in the Dogu config, no version comparison.
+2. Order: config, then `ALTER USER`, then the marker — an aborted rotation is retried.
+3. Runs after `startPostgresql`, because `ALTER USER` needs a running DB. On the Unix socket `trust` applies, so the old password is not needed.
+4. Never reached in the restore case — there `initAdmin` sets password and marker.
 
 ### Startup (`resources/startup.sh`)
 
 `startup.sh` waits as long as `local_state=upgrading` is set.
+If `PGDATA` is empty, `initAdmin` additionally sets `password_rotated=true`, because a freshly generated password is safe. 
 After that, it starts `/usr/local/bin/docker-entrypoint.sh` with Dogu-specific parameters.
 
 Important:
diff --git a/resources/post-upgrade.sh b/resources/post-upgrade.sh
index 9fe3bad..47b53d2 100755
--- a/resources/post-upgrade.sh
+++ b/resources/post-upgrade.sh
@@ -9,6 +9,40 @@ source "/usr/local/bin/docker-entrypoint.sh"
 
 : "${PGDATA:?PGDATA is not set. Abort post-upgrade as the script needs the environment variable.}"
 
+# rotateSuperuserPassword replaces the superuser password once, because it may have been generated by
+# a doguctl older than v0.12.2 which used math/rand instead of crypto/rand. Affected values cannot be
+# told apart from safe ones, so the rotation is unconditional and guarded by a config marker only.
+function rotateSuperuserPassword() {
+  local alreadyRotated
+  alreadyRotated=$(doguctl config --default "false" "password_rotated")
+
+  if [[ "${alreadyRotated}" == "true" ]]; then
+    echo "Superuser password has already been rotated; skipping"
+    return 0
+  fi
+
+  echo "Rotating superuser password..."
+
+  local postgresUser
+  postgresUser=$(doguctl config --default "postgres" user)
+
+  local newPassword
+  newPassword=$(doguctl random)
+
+  # The config is written first: the new password must never exist in the database alone.
+  doguctl config --encrypted password "${newPassword}"
+
+  psql \
+    --variable=ON_ERROR_STOP=1 \
+    --username="${postgresUser}" \
+    --command="ALTER USER \"${postgresUser}\" WITH PASSWORD '${newPassword}';"
+
+  # The marker is written last, so an aborted rotation is retried on the next upgrade.
+  doguctl config "password_rotated" "true"
+
+  echo "Superuser password rotated"
+}
+
 function startPostgresql() {
   echo "starting postgresql temporary"
   docker_temp_server_start postgres
@@ -89,6 +123,7 @@ function runPostUpgrade() {
     fi
 
     startPostgresql
+    rotateSuperuserPassword
     runMigrations
     stopPostgresql
 
diff --git a/resources/startup.sh b/resources/startup.sh
index 38673d8..7b963d6 100755
--- a/resources/startup.sh
+++ b/resources/startup.sh
@@ -34,6 +34,10 @@ function initAdmin() {
 
   # store the password encrypted
   doguctl config -e password "${postgres_psw}"
+
+  # A freshly generated password is safe by definition, so the rotation marker is set right away and
+  # rotateSuperuserPassword in post-upgrade.sh never runs on this instance.
+  doguctl config "password_rotated" "true"
 }
 
 function mask2cidr() {
diff --git a/resources/util.sh b/resources/util.sh
index 679a999..07ecd57 100644
--- a/resources/util.sh
+++ b/resources/util.sh
@@ -58,4 +58,4 @@ function versionXLessOrEqualThanY() {
   fi
 
   return 1
-}
\ No newline at end of file
+}