Invalidate existing sessions on password change/reset (B-34)

Neither self-service password change nor the admin reset invalidated
already-issued JWTs — a 24h-lifetime token stayed valid regardless, so
a stolen token (or an attacker who already had the old password) kept
working past a password change meant to lock them out. The admin reset
exists precisely for the "account compromised" case and didn't evict
the attacker at all.

Add User.token_version (migration 943dbd74d983), embedded in every JWT
as a "tv" claim and checked against the DB on every request in
get_current_user/get_optional_user; a mismatch reads as session_expired.
Both change-password and the admin reset bump it. change-password hands
back a freshly minted token so the caller's own session keeps working
instead of being logged out by its own request; the admin reset does
not, since that session isn't the one making the call.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

BUGS.md

@@ -1,11 +1,11 @@
 # Known bugs
 
 A second full-codebase audit on 2026-07-27 found **25 further issues** (4 critical, 6 high,
-7 medium, 8 low), listed below as B-33 … B-49. B-25 through B-33 are fixed (see "Previously
+7 medium, 8 low), listed below as B-33 … B-49. B-25 through B-34 are fixed (see "Previously
-fixed" below) — no Critical-severity finding remains open; the other 16 are High/Medium/Low.
+fixed" below) — no Critical-severity finding remains open; the other 15 are High/Medium/Low.
 The 139-test suite was green at the time of the audit, so none of these were caught by existing
-coverage — every fix lands with a regression test (the nine fixes so far brought the suite
+coverage — every fix lands with a regression test (the ten fixes so far brought the suite
-from 139 to 192).
+from 139 to 194).
 
 The recurring pattern across the open findings is worth stating once: the code is rigorous
 about the failure modes that have actually been hit, and silent about the ones that have not.
@@ -18,21 +18,6 @@ single-process assumptions, no user-facing history, etc.), see "Known gaps / TOD
 
 ---
 
-## High
-
-### B-34 — Password change and admin reset do not invalidate existing sessions
-
-Neither `/users/me/change-password` nor `/admin/users/{id}/reset-password` invalidates
-already-issued JWTs (24h default lifetime, no revocation, no `token_version` on the user). The
-admin reset exists precisely for the "account compromised" case and **does not evict the
-attacker**.
-
-**Proposed fix.** Add a `token_version` (or `password_changed_at`) column on `User`, embed it
-in the JWT claims, and reject any token whose value is stale in
-`auth/dependencies.py:get_current_user`. Bump it on both endpoints.
-
----
-
 ## Medium
 
 ### B-35 — Every API timestamp is naive, so the frontend renders it in the wrong timezone
@@ -212,9 +197,10 @@ already does.
 - **B-31** — resubscribing on reconnect ran serially before anything else started, freezing the chain tip (and so an in-flight draw) for the whole sweep
 - **B-32** — an RBF bump's fee delta could fall below BIP125's relay-mandated minimum, so the node rejected it and the same tick retried identically forever; also had no ceiling on how high the fee rate could climb
 - **B-33** — `POST /auth/login` had no rate limiting on a custodial wallet, so a patient distributed attack could brute-force a password against an enumerable username list; fixed with per-username *and* per-IP exponential backoff (`app/auth/rate_limit.py`), registration throttled per-IP too (also bounds B-31's attacker-controlled user count)
+- **B-34** — neither self-service password change nor the admin reset invalidated already-issued JWTs, so a stolen token (or an attacker's own session) survived a password change meant to lock it out; fixed with a `User.token_version` column embedded in every JWT (`"tv"` claim) and checked on every request in `get_current_user`/`get_optional_user`, bumped on both endpoints — change-password hands back a fresh token so the caller's own session keeps working, the admin reset does not
 
 See git history for the fix-by-fix breakdown (commits `f13f685`, `50a43ae`, `933760e`, and the
-B-28/B-29/B-30/B-31/B-32/B-33 fixes). Suite grew from 139 to 192 tests over the nine.
+B-28/B-29/B-30/B-31/B-32/B-33/B-34 fixes). Suite grew from 139 to 194 tests over the ten.
 
 A full-codebase audit on 2026-07-26 (commit `d4e0974`) found 24 bugs across every Python
 module under `app/`, both static frontends, and the Docker/Caddy deployment — 5 critical,

app/api/routes/admin.py

@@ -215,6 +215,11 @@ async def reset_user_password(
 
     new_password = secrets.token_urlsafe(12)
     user.password_hash = hash_password(new_password)
+    # B-34: this endpoint exists precisely for the "account compromised" case —
+    # without bumping token_version, whoever was already logged in (the
+    # attacker, if that's who prompted the reset) stayed logged in on their
+    # existing token until it naturally expired, unaffected by the reset.
+    user.token_version += 1
     await write_audit_log(session, "admin_password_reset", {"user_id": user_id}, user_id=user_id)
     await session.commit()
     return AdminPasswordResetResponse(username=user.username, new_password=new_password)

app/api/routes/users.py

@@ -5,7 +5,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.errors import http_error
 from app.auth.dependencies import get_current_user
-from app.auth.security import MIN_PASSWORD_LENGTH, hash_password, verify_password
+from app.auth.security import MIN_PASSWORD_LENGTH, create_access_token, hash_password, verify_password
 from app.db.models import Round, RoundParticipant, User
 from app.db.session import get_session
 from app.wallet.balance import compute_pending_balance
@@ -45,12 +45,16 @@ class ChangePasswordRequest(BaseModel):
     new_password: str
 
 
-@router.post("/me/change-password", status_code=status.HTTP_204_NO_CONTENT)
+class ChangePasswordResponse(BaseModel):
+    access_token: str
+
+
+@router.post("/me/change-password", response_model=ChangePasswordResponse)
 async def change_password(
     body: ChangePasswordRequest,
     user: User = Depends(get_current_user),
     session: AsyncSession = Depends(get_session),
-) -> None:
+) -> ChangePasswordResponse:
     """Self-service password change — requires the current password, unlike the
     admin-only /admin/users/{id}/reset-password (which is for a user who's
     actually locked out and can't provide it)."""
@@ -67,7 +71,15 @@ async def change_password(
         )
 
     user.password_hash = hash_password(body.new_password)
+    # B-34: bumping token_version invalidates every token issued before this
+    # point — including this very request's own bearer token, and any an
+    # attacker who knew the old password might be holding. A fresh token is
+    # handed back so *this* session keeps working without forcing a re-login;
+    # every other open session (this user's other devices, or an attacker's)
+    # gets "session_expired" on its next request.
+    user.token_version += 1
     await session.commit()
+    return ChangePasswordResponse(access_token=create_access_token(user.id, user.token_version))
 
 
 class LastRoundResultResponse(BaseModel):

app/auth/dependencies.py

@@ -16,13 +16,19 @@ async def get_current_user(
     session: AsyncSession = Depends(get_session),
 ) -> User:
     try:
-        user_id = decode_access_token(credentials.credentials)
+        user_id, token_version = decode_access_token(credentials.credentials)
     except Exception as exc:
         raise http_error(status.HTTP_401_UNAUTHORIZED, "session_expired", "invalid token") from exc
 
     user = await session.scalar(select(User).where(User.id == user_id))
     if user is None:
         raise http_error(status.HTTP_401_UNAUTHORIZED, "session_expired", "user not found")
+    if user.token_version != token_version:
+        # B-34: a password change (self-service or admin reset) bumps
+        # token_version, so a token issued before it — including one an
+        # attacker who had the old password is still holding — reads as
+        # expired rather than staying valid until it naturally times out.
+        raise http_error(status.HTTP_401_UNAUTHORIZED, "session_expired", "token has been superseded")
     return user
 
 
@@ -37,7 +43,10 @@ async def get_optional_user(
     if not auth_header.startswith("Bearer "):
         return None
     try:
-        user_id = decode_access_token(auth_header.removeprefix("Bearer "))
+        user_id, token_version = decode_access_token(auth_header.removeprefix("Bearer "))
     except Exception:
         return None
-    return await session.scalar(select(User).where(User.id == user_id))
+    user = await session.scalar(select(User).where(User.id == user_id))
+    if user is None or user.token_version != token_version:
+        return None
+    return user

app/auth/routes.py

@@ -111,7 +111,9 @@ async def register(
             continue
         await session.refresh(user)
         request.app.state.electrum_listener.address_for_new_user(user.id, user.address)
-        return TokenResponse(access_token=create_access_token(user.id), address=user.address)
+        return TokenResponse(
+            access_token=create_access_token(user.id, user.token_version), address=user.address
+        )
 
     raise http_error(
         status.HTTP_409_CONFLICT,
@@ -148,4 +150,6 @@ async def login(
     # on its own, so one correct login can't be used to wipe out an IP's failure
     # count while it's mid-attack against other accounts.
     limiters.login.record_success(username_key)
-    return TokenResponse(access_token=create_access_token(user.id), address=user.address)
+    return TokenResponse(
+        access_token=create_access_token(user.id, user.token_version), address=user.address
+    )

app/auth/security.py

@@ -39,12 +39,20 @@ def verify_password(password: str, password_hash: str) -> bool:
         return False
 
 
-def create_access_token(user_id: int) -> str:
+def create_access_token(user_id: int, token_version: int = 0) -> str:
     expires_at = datetime.now(timezone.utc) + timedelta(minutes=settings.jwt_expire_minutes)
-    payload = {"sub": str(user_id), "exp": expires_at}
+    # "tv" lets get_current_user (app/auth/dependencies.py) reject a token issued
+    # before the account's password was last changed (B-34): change-password and
+    # the admin reset both bump User.token_version, so every token that still
+    # carries the old value stops working immediately instead of staying valid
+    # for up to jwt_expire_minutes after a compromise is supposedly handled.
+    payload = {"sub": str(user_id), "tv": token_version, "exp": expires_at}
     return jwt.encode(payload, settings.jwt_secret, algorithm=settings.jwt_algorithm)
 
 
-def decode_access_token(token: str) -> int:
+def decode_access_token(token: str) -> tuple[int, int]:
     payload = jwt.decode(token, settings.jwt_secret, algorithms=[settings.jwt_algorithm])
-    return int(payload["sub"])
+    # .get(..., 0) covers tokens issued before "tv" existed (pre-B-34 deploy) —
+    # they carry no claim at all, and 0 is what a freshly migrated user's
+    # token_version starts at, so those sessions keep working across the deploy.
+    return int(payload["sub"]), int(payload.get("tv", 0))

app/db/models.py

@@ -21,6 +21,12 @@ class User(Base):
     # Read cache only; must always be written in the same transaction as the
     # utxo_events rows it summarizes. Source of truth is utxo_events.
     cached_balance_sats: Mapped[int] = mapped_column(BigInteger, default=0)
+    # Embedded in every issued JWT (app/auth/security.py) and checked on every
+    # request (app/auth/dependencies.py:get_current_user). Bumped on a
+    # self-service or admin password change so every token issued before that
+    # point stops working immediately, instead of staying valid for up to
+    # jwt_expire_minutes after a compromised account's password is reset (B-34).
+    token_version: Mapped[int] = mapped_column(default=0, server_default="0")
     created_at: Mapped[datetime] = mapped_column(default=utcnow)
 
 

app/static/app.js

@@ -749,10 +749,15 @@ async function changePassword() {
 
   await withLoading(btn, t('loading.updating'), async () => {
     try {
-      await call('POST', '/users/me/change-password', {
+      const data = await call('POST', '/users/me/change-password', {
         current_password: currentPassword,
         new_password: newPassword,
       });
+      // The server just invalidated every previously issued token (B-34) —
+      // including the one this very request was authenticated with — and
+      // handed back a fresh one so this tab doesn't get logged out too.
+      token = data.access_token;
+      localStorage.setItem('plm_token', token);
       document.getElementById('settings-current-password').value = '';
       document.getElementById('settings-new-password').value = '';
       document.getElementById('settings-new-password-confirm').value = '';

migrations/versions/943dbd74d983_add_token_version_to_users.py

@@ -0,0 +1,40 @@
+"""add token_version to users
+
+Revision ID: 943dbd74d983
+Revises: 861e76aaf34c
+Create Date: 2026-07-27
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '943dbd74d983'
+down_revision: Union[str, Sequence[str], None] = '861e76aaf34c'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # server_default backfills every existing user to 0 (their current sessions
+    # stay valid, since 0 also matches what already-issued tokens carry
+    # implicitly — see the "sub"-only tokens issued before this migration);
+    # dropped right after so new rows go through the ORM default instead of a
+    # stale constant.
+    op.add_column(
+        'users', sa.Column('token_version', sa.Integer(), nullable=False, server_default='0')
+    )
+    with op.batch_alter_table('users') as batch_op:
+        batch_op.alter_column('token_version', server_default=None)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column('users', 'token_version')
+    # ### end Alembic commands ###

tests/unit/test_admin.py

@@ -205,6 +205,10 @@ async def test_admin_resets_user_password(client):
         assert refreshed.password_hash != old_hash
         assert verify_password(new_password, refreshed.password_hash)
         assert not verify_password("original-password", refreshed.password_hash)
+        # B-34: the reset must bump token_version so a session opened before
+        # the reset (e.g. an attacker who had the old password) is evicted
+        # immediately rather than staying valid until the JWT naturally expires.
+        assert refreshed.token_version == 1
 
 
 async def test_admin_reset_password_requires_token(client):

tests/unit/test_security.py

@@ -9,8 +9,21 @@ def test_password_hash_roundtrip():
 
 def test_jwt_roundtrip(monkeypatch):
     monkeypatch.setattr(security.settings, "jwt_secret", "test-secret")
-    token = security.create_access_token(user_id=42)
+    token = security.create_access_token(user_id=42, token_version=3)
-    assert security.decode_access_token(token) == 42
+    assert security.decode_access_token(token) == (42, 3)
+
+
+def test_jwt_decode_defaults_token_version_for_tokens_issued_before_it_existed(monkeypatch):
+    """B-34: a token minted before the "tv" claim existed has no such key at
+    all. It must still decode — as token_version 0, matching a freshly
+    migrated user's starting value — rather than raising or being treated as
+    permanently stale."""
+    import jwt as pyjwt
+
+    monkeypatch.setattr(security.settings, "jwt_secret", "test-secret")
+    payload = {"sub": "42"}
+    token = pyjwt.encode(payload, "test-secret", algorithm=security.settings.jwt_algorithm)
+    assert security.decode_access_token(token) == (42, 0)
 
 
 def test_verify_password_returns_false_for_an_unparseable_hash():

tests/unit/test_users.py

@@ -81,7 +81,8 @@ async def test_change_password_updates_login(client):
         headers=headers,
         json={"current_password": "original-password", "new_password": "brand-new-password"},
     )
-    assert resp.status_code == 204
+    assert resp.status_code == 200
+    assert resp.json()["access_token"]
 
     resp = await client.post("/auth/login", json={"username": "alice", "password": "original-password"})
     assert resp.status_code == 401
@@ -90,6 +91,36 @@ async def test_change_password_updates_login(client):
     assert resp.status_code == 200
 
 
+async def test_change_password_invalidates_the_old_token_but_not_the_new_one(client):
+    """B-34: neither self-service change-password nor the admin reset used to
+    invalidate already-issued JWTs, so a stolen token (or an attacker who
+    already had the old password) stayed logged in until the token's natural
+    24h expiry — even past a password change meant to lock them out."""
+    old_token = await _register(client)
+    old_headers = {"Authorization": f"Bearer {old_token}"}
+
+    resp = await client.post(
+        "/users/me/change-password",
+        headers=old_headers,
+        json={"current_password": "original-password", "new_password": "brand-new-password"},
+    )
+    assert resp.status_code == 200
+    new_token = resp.json()["access_token"]
+    assert new_token != old_token
+
+    # The old token (what an attacker holding the old password would still
+    # have) is now rejected...
+    resp = await client.get("/users/me", headers=old_headers)
+    assert resp.status_code == 401
+    assert resp.json()["detail"]["code"] == "session_expired"
+
+    # ...but the freshly issued one keeps this same session working, so the
+    # user who just changed their own password isn't logged out too.
+    new_headers = {"Authorization": f"Bearer {new_token}"}
+    resp = await client.get("/users/me", headers=new_headers)
+    assert resp.status_code == 200
+
+
 async def test_change_password_rejects_too_short(client):
     token = await _register(client)
     headers = {"Authorization": f"Bearer {token}"}