Block the whole network for a flagged signup, not just its /32

register_ip_block always blocked the exact signup IP as a /32 (or /128
for v6), which is close to pointless for the datacenter/VPN/proxy space
these flags fire on: a repeat bad actor from the same provider almost
never reuses the exact same address, but very often reuses a different
one in the same block.

classify_signup_ip now returns a fourth value, block_cidr — ipapi.is's
asn.route CIDR when it's a valid network that actually contains the
signup IP (already being tracked in ipapi_range_cache purely for lookup
caching), falling back to the address's own /32 or /128 when no usable
route exists. register_ip_block blocks that instead of always deriving
a /32 itself.

Added range_cache_tests() covering the cache/fallback logic directly
(pure sqlite + ipaddress, no network), and updated the existing
ip_scrutiny_tests()/combined_signal_tests() mocks for the new 4-tuple
classify_signup_ip return and register_ip_block arity.

.env.example

@@ -105,8 +105,13 @@ IP_SCRUTINY_HOLD_WELCOME=true
 # signup IP was flagged.
 IP_SCRUTINY_ABUSE_THRESHOLD=1
 
-# Auto-register a flagged IP into Mastodon's native Admin::IpBlock. Requires
+# Auto-register a flagged signup's network into Mastodon's native
-# the ABUSE_BOT_TOKEN to carry the admin:write:ip_blocks scope (see
+# Admin::IpBlock — ipapi.is's asn.route CIDR when it's a valid network that
+# actually contains the signup IP, else just that one /32 or /128. Blocking
+# the whole network matters here because a flagged signup is almost always
+# datacenter/VPN/proxy space, where a repeat bad actor is far more likely to
+# come back from a different address in the same block than the exact one.
+# Requires the ABUSE_BOT_TOKEN to carry the admin:write:ip_blocks scope (see
 # CLAUDE.md's moderator-token-gotcha section) — without it this 403s and is
 # logged as an error, but nothing else in the bot is affected.
 IP_SCRUTINY_AUTO_IPBLOCK=true

README.md

@@ -72,10 +72,16 @@ Every `account.created` delivery already carries the signup IP for free
      on `account.created` and only sent when `account.approved` fires, i.e.
      once a human clears yttrx's existing approval-required registration
      gate. If the signup is rejected instead, no welcome is ever sent.
-   - **Auto-registered IP block** (`IP_SCRUTINY_AUTO_IPBLOCK`) — the IP is
+   - **Auto-registered IP block** (`IP_SCRUTINY_AUTO_IPBLOCK`) — the *network*
+     the signup IP belongs to (ipapi.is's `asn.route`, when it's a valid CIDR
+     that actually contains the IP; otherwise just that one `/32`/`/128`) is
      added to Mastodon's native `Admin::IpBlock` at
      `IP_SCRUTINY_IPBLOCK_SEVERITY` (default `sign_up_requires_approval`,
-     reversible from the admin UI).
+     reversible from the admin UI). Blocking the whole network rather than
+     the single address matters here specifically because a flagged signup is
+     almost always datacenter/VPN/proxy space — a repeat bad actor is far more
+     likely to come back from a different address in the same block than the
+     exact one, unlike a residential IP where that reasoning wouldn't hold.
    - **Lowered abuse-bot threshold** — if this account is later reported, the
      usual `ABUSE_SOURCES_*` distinct-reporter threshold is replaced by
      `IP_SCRUTINY_ABUSE_THRESHOLD` (whichever is lower), since a flagged
@@ -211,7 +217,7 @@ Copy `.env.example` to `.env` and fill in:
 | `IP_SCRUTINY_DRY_RUN` | `true` — classify + DM only, no held welcome, no ip_block write |
 | `IP_SCRUTINY_HOLD_WELCOME` | `true` — hold the welcome for a flagged signup until `account.approved` |
 | `IP_SCRUTINY_ABUSE_THRESHOLD` | Distinct-reporter threshold used (if lower) for accounts with a flagged signup IP |
-| `IP_SCRUTINY_AUTO_IPBLOCK` | Auto-register a flagged IP into Mastodon's `Admin::IpBlock` |
+| `IP_SCRUTINY_AUTO_IPBLOCK` | Auto-register a flagged signup's network (ipapi.is route, or its own `/32`/`/128` if no route) into Mastodon's `Admin::IpBlock` |
 | `IP_SCRUTINY_IPBLOCK_SEVERITY` | `sign_up_requires_approval` (default), `sign_up_block`, or `no_access` |
 | `CHECK_MAIL_ENABLED` | Master switch for disposable/high-risk email signup scrutiny |
 | `CHECK_MAIL_API_KEY` | check-mail.org API key; blank disables the check |

app/main.py

@@ -136,7 +136,13 @@ IP_SCRUTINY_HOLD_WELCOME = os.environ.get("IP_SCRUTINY_HOLD_WELCOME", "true").lo
 # Distinct-reporter threshold used INSTEAD of the tier's usual threshold (via
 # min()) when the reported account's signup IP was flagged.
 IP_SCRUTINY_ABUSE_THRESHOLD = int(os.environ.get("IP_SCRUTINY_ABUSE_THRESHOLD", "1"))
-# Auto-register flagged IPs into Mastodon's native Admin::IpBlock.
+# Auto-register a flagged signup's network into Mastodon's native
+# Admin::IpBlock. Blocks the ASN/route-level CIDR ipapi.is reports the IP
+# belonging to (see classify_signup_ip's block_cidr), not just the single
+# address — a flagged signup is almost always datacenter/VPN/proxy space, and
+# a repeat bad actor is far more likely to come back from a different address
+# in the same block than the exact same one. Falls back to a single-address
+# (/32 or /128) block if no usable route was returned/cached.
 IP_SCRUTINY_AUTO_IPBLOCK = os.environ.get("IP_SCRUTINY_AUTO_IPBLOCK", "true").lower() in ("1", "true", "yes")
 # severity: sign_up_requires_approval | sign_up_block | no_access
 IP_SCRUTINY_IPBLOCK_SEVERITY = os.environ.get("IP_SCRUTINY_IPBLOCK_SEVERITY", "sign_up_requires_approval")
@@ -403,7 +409,7 @@ def cached_ip_intel(ip: str) -> dict | None:
     family, packed, _, _ = bounds
     with _db() as conn:
         row = conn.execute(
-            "SELECT is_datacenter, is_vpn, is_proxy, is_tor, is_abuser, org "
+            "SELECT is_datacenter, is_vpn, is_proxy, is_tor, is_abuser, org, cidr "
             "FROM ipapi_range_cache "
             "WHERE family = ? AND range_start <= ? AND range_end >= ? LIMIT 1",
             (family, packed, packed),
@@ -414,6 +420,7 @@ def cached_ip_intel(ip: str) -> dict | None:
             "is_datacenter": bool(row[0]), "is_vpn": bool(row[1]),
             "is_proxy": bool(row[2]), "is_tor": bool(row[3]),
             "is_abuser": bool(row[4]), "org": row[5] or "",
+            "cidr": row[6] or bounds[3],
         }
 
 
@@ -627,14 +634,14 @@ def process_signup(account_id: str, acct: str, ip: str, email: str = "",
     email_flagged = False
 
     if IP_SCRUTINY_ENABLED and ip:
-        classification, org, ip_flagged = classify_signup_ip(ip)
+        classification, org, ip_flagged, block_cidr = classify_signup_ip(ip)
         record_signup_ip(account_id, acct, ip, classification, org, ip_flagged)
 
         if ip_flagged:
             log.warning("flagged signup acct=%s ip=%s classification=%s org=%s",
                         acct, ip, classification, org)
             if IP_SCRUTINY_AUTO_IPBLOCK and not IP_SCRUTINY_DRY_RUN:
-                register_ip_block(ip, acct, org)
+                register_ip_block(ip, acct, org, block_cidr)
                 mark_ipblock_registered(account_id)
             prefix = "[DRY-RUN] " if IP_SCRUTINY_DRY_RUN else ""
             reasons.append(f"{prefix}IP {ip} ({org or 'unknown org'}, {classification})")
@@ -844,16 +851,21 @@ def classify_account(target_id: str) -> dict:
     }
 
 
-def classify_signup_ip(ip: str) -> tuple[str, str, bool]:
+def classify_signup_ip(ip: str) -> tuple[str, str, bool, str]:
     """Classify a signup IP via ipapi.is, cached indefinitely in sqlite (an
     IP's owning org/abuse posture doesn't change on the timescale that
     matters here).
 
-    Returns (classification, org, flagged). classification is a "+"-joined
+    Returns (classification, org, flagged, block_cidr). classification is a
-    list of every matched signal (datacenter/vpn/proxy/tor/abuser), or
+    "+"-joined list of every matched signal (datacenter/vpn/proxy/tor/abuser),
-    "clean" if none matched. flagged is True if any signal matched. API
+    or "clean" if none matched. flagged is True if any signal matched.
-    failure yields ("unknown", "", False) — scrutiny should never trigger on
+    block_cidr is the network register_ip_block should block when flagged —
-    our own lookup errors.
+    ipapi.is's asn.route when it's a valid network that actually contains ip,
+    else ip's own /32 or /128 — since a flagged signup is almost always
+    datacenter/VPN/proxy space, where a repeat bad actor is far more likely to
+    come back from a different address in the same block than the exact same
+    one. API failure yields ("unknown", "", False, "<ip>/32|128") — scrutiny
+    should never trigger on our own lookup errors.
     """
     intel = cached_ip_intel(ip)
     if intel is None:
@@ -866,7 +878,8 @@ def classify_signup_ip(ip: str) -> tuple[str, str, bool]:
             data = resp.json()
         except (httpx.HTTPError, ValueError) as exc:
             log.warning("ipapi.is lookup failed for ip=%s: %s", ip, exc)
-            return "unknown", "", False
+            bounds = _ip_range_bounds(ip)
+            return "unknown", "", False, bounds[3] if bounds else f"{ip}/32"
         intel = {
             "is_datacenter": bool(data.get("is_datacenter")),
             "is_vpn": bool(data.get("is_vpn")),
@@ -877,6 +890,8 @@ def classify_signup_ip(ip: str) -> tuple[str, str, bool]:
                     or (data.get("asn") or {}).get("org") or ""),
         }
         route = (data.get("asn") or {}).get("route") or ""
+        bounds = _ip_range_bounds(ip, route)
+        intel["cidr"] = bounds[3] if bounds else f"{ip}/32"
         cache_ip_intel(ip, intel, route)
 
     reasons = [name for name, key in (
@@ -887,17 +902,25 @@ def classify_signup_ip(ip: str) -> tuple[str, str, bool]:
         ("abuser", "is_abuser"),
     ) if intel[key]]
     classification = "+".join(reasons) if reasons else "clean"
-    return classification, intel["org"], bool(reasons)
+    return classification, intel["org"], bool(reasons), intel.get("cidr") or f"{ip}/32"
 
 
-def register_ip_block(ip: str, acct: str, org: str) -> None:
+def register_ip_block(ip: str, acct: str, org: str, cidr: str = "") -> None:
-    """Register a flagged signup IP in Mastodon's native Admin::IpBlock."""
+    """Register a flagged signup's network in Mastodon's native Admin::IpBlock.
-    try:
+
-        prefix_len = 32 if ipaddress.ip_address(ip).version == 4 else 128
+    cidr should be classify_signup_ip's block_cidr — the ASN/route-level
-    except ValueError:
+    network the signup IP belongs to, so a repeat bad actor from the same
-        log.warning("skipping ip_block registration for unparseable ip=%r (acct=%s)", ip, acct)
+    datacenter/VPN/proxy block is blocked too, not just this one address.
-        return
+    Falls back to a single-address block if no cidr is given or ip itself
-    cidr = f"{ip}/{prefix_len}"
+    doesn't parse (defensive only; classify_signup_ip always supplies one).
+    """
+    if not cidr:
+        try:
+            prefix_len = 32 if ipaddress.ip_address(ip).version == 4 else 128
+        except ValueError:
+            log.warning("skipping ip_block registration for unparseable ip=%r (acct=%s)", ip, acct)
+            return
+        cidr = f"{ip}/{prefix_len}"
     comment = f"welcomebot: flagged signup @{acct} ({org or 'unknown org'})"[:200]
     try:
         resp = httpx.post(

test_local.py

@@ -224,7 +224,7 @@ def ip_scrutiny_tests():
     ipblocks = []
     main.send_welcome = lambda account_id, acct: sent.append((account_id, acct))
     main.dm_moderator = lambda message: dms.append(message)
-    main.register_ip_block = lambda ip, acct, org: ipblocks.append((ip, acct, org))
+    main.register_ip_block = lambda ip, acct, org, cidr: ipblocks.append((ip, acct, org, cidr))
     # A flagged-but-not-held signup starts the suspicious watch inline, which
     # would otherwise hit the network for a baseline snapshot — stub it.
     main.fetch_account_counts = lambda account_id: (0, 0)
@@ -233,9 +233,9 @@ def ip_scrutiny_tests():
         return classifications[ip]
 
     classifications = {
-        "203.0.113.10": ("clean", "Example Residential ISP", False),
+        "203.0.113.10": ("clean", "Example Residential ISP", False, "203.0.113.10/32"),
-        "198.51.100.20": ("datacenter", "Example Cloud Hosting Inc", True),
+        "198.51.100.20": ("datacenter", "Example Cloud Hosting Inc", True, "198.51.100.0/24"),
-        "198.51.100.21": ("datacenter", "Example Cloud Hosting Inc", True),
+        "198.51.100.21": ("datacenter", "Example Cloud Hosting Inc", True, "198.51.100.0/24"),
     }
     main.classify_signup_ip = classify
 
@@ -256,7 +256,7 @@ def ip_scrutiny_tests():
     sent.clear(); dms.clear(); ipblocks.clear()
     main.process_signup("102", "dc1", "198.51.100.20")
     assert ("102", "dc1") not in sent, "welcome should be held for a flagged signup"
-    assert ipblocks == [("198.51.100.20", "dc1", "Example Cloud Hosting Inc")], ipblocks
+    assert ipblocks == [("198.51.100.20", "dc1", "Example Cloud Hosting Inc", "198.51.100.0/24")], ipblocks
     assert any("dc1" in d and "held" in d for d in dms), dms
     assert main.get_signup_flag("102") is True
 
@@ -268,7 +268,7 @@ def ip_scrutiny_tests():
     #     fire, so process_signup must welcome + start the watch immediately
     #     instead of waiting for an event that isn't coming.
     sent.clear(); dms.clear(); ipblocks.clear()
-    classifications["198.51.100.22"] = ("datacenter", "Example Cloud Hosting Inc", True)
+    classifications["198.51.100.22"] = ("datacenter", "Example Cloud Hosting Inc", True, "198.51.100.0/24")
     main.process_signup("104", "dc3", "198.51.100.22", "", True)
     assert ("104", "dc3") in sent, "already-approved flagged signup must be welcomed immediately"
     assert main.get_signup_flag("104") is True
@@ -404,6 +404,45 @@ def email_scrutiny_tests():
     assert domain_blocks == [], domain_blocks
 
 
+def range_cache_tests():
+    """Drive the ipapi range-cache helpers (_ip_range_bounds/cache_ip_intel/
+    cached_ip_intel) directly — pure sqlite + ipaddress logic, no network.
+    This is what classify_signup_ip's block_cidr (the network register_
+    ip_block blocks) is built on."""
+    intel = {
+        "is_datacenter": True, "is_vpn": False, "is_proxy": False,
+        "is_tor": False, "is_abuser": False, "org": "Example Cloud Hosting Inc",
+    }
+
+    # A. a valid route containing the ip caches (and returns) the wider CIDR,
+    #    not just the single address.
+    main.cache_ip_intel("198.51.100.77", intel, route="198.51.100.0/24")
+    cached = main.cached_ip_intel("198.51.100.77")
+    assert cached["cidr"] == "198.51.100.0/24", cached
+    assert cached["is_datacenter"] is True
+
+    # B. any other address in that same cached range hits the cache with the
+    #    same wider CIDR — this is the point of range-based caching, and
+    #    exactly what lets a repeat signup from elsewhere in the block also
+    #    resolve to blocking the whole range.
+    cached2 = main.cached_ip_intel("198.51.100.200")
+    assert cached2["cidr"] == "198.51.100.0/24", cached2
+
+    # C. an address outside the cached range is a cache miss.
+    assert main.cached_ip_intel("198.51.101.1") is None
+
+    # D. a route that doesn't actually contain the ip falls back to a /32 —
+    #    never trust a route wide enough to not even cover the IP it came from.
+    main.cache_ip_intel("203.0.113.9", intel, route="10.0.0.0/8")
+    cached3 = main.cached_ip_intel("203.0.113.9")
+    assert cached3["cidr"] == "203.0.113.9/32", cached3
+
+    # E. no route at all -> /32.
+    main.cache_ip_intel("203.0.113.10", intel, route="")
+    cached4 = main.cached_ip_intel("203.0.113.10")
+    assert cached4["cidr"] == "203.0.113.10/32", cached4
+
+
 def combined_signal_tests():
     """Drive process_signup's combined IP+email immediate-suspend path
     (SUSPICIOUS_COMBINED_*), independent of the OR-based hourly sweep."""
@@ -415,7 +454,7 @@ def combined_signal_tests():
     main.send_welcome = lambda account_id, acct: sent.append((account_id, acct))
     main.dm_moderator = lambda message: dms.append(message)
     main.apply_action = lambda target_id, action, text: actions.append((target_id, action))
-    main.register_ip_block = lambda ip, acct, org: ipblocks.append((ip, acct, org))
+    main.register_ip_block = lambda ip, acct, org, cidr: ipblocks.append((ip, acct, org, cidr))
     main.register_email_domain_block = lambda domain, acct: domain_blocks.append((domain, acct))
     main.fetch_account_counts = lambda account_id: (0, 0)
 
@@ -434,8 +473,8 @@ def combined_signal_tests():
     main.ABUSE_ALLOWLIST = {"trustedstaff"}
 
     ip_classifications = {
-        "198.51.100.40": ("datacenter", "Example Cloud Hosting Inc", True),
+        "198.51.100.40": ("datacenter", "Example Cloud Hosting Inc", True, "198.51.100.32/28"),
-        "198.51.100.41": ("datacenter", "Example Cloud Hosting Inc", True),
+        "198.51.100.41": ("datacenter", "Example Cloud Hosting Inc", True, "198.51.100.32/28"),
     }
     main.classify_signup_ip = lambda ip: ip_classifications[ip]
     email_classifications = {
@@ -456,7 +495,7 @@ def combined_signal_tests():
             "SELECT 1 FROM suspicious_watch WHERE account_id = ?", ("501",),
         ).fetchone()
     assert row is None, "an immediately-suspended signup must not also enter the hourly watch"
-    assert ("198.51.100.40", "bothbad", "Example Cloud Hosting Inc") in ipblocks, ipblocks
+    assert ("198.51.100.40", "bothbad", "Example Cloud Hosting Inc", "198.51.100.32/28") in ipblocks, ipblocks
     assert ("temp-mail.org", "bothbad") in domain_blocks, domain_blocks
 
     # B. only IP flagged -> untouched by the combined path, falls through to
@@ -643,6 +682,7 @@ if __name__ == "__main__":
     policy_tests()
     ip_scrutiny_tests()
     email_scrutiny_tests()
+    range_cache_tests()
     combined_signal_tests()
     suspicious_watch_tests()
     suspicious_sweep_tests()