jens
f69aa18bec
nsupdate.php/nsupdate_ipv4.php/nsupdate_ipv6.php pass unsanitized $_GET input straight into exec()'d shell commands. Gated by Apache Basic Auth on the dyndns vhost, so not anonymously exploitable, but a real OS command injection reachable by anyone with valid (or leaked) dyndns credentials. Documents the finding and the fix approach; not yet applied.
170 lines
11 KiB
Markdown
170 lines
11 KiB
Markdown
# alpha.jayfield.org — TODO
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Outstanding hardening items (see `README.md` for the full service overview).
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Everything below is low-risk/no-downtime **except the item marked
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HIGH PRIORITY**.
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- [ ] **HIGH PRIORITY — OS command injection in the dyndns update scripts** — found 2026-07-20
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`/var/www/dyndns/nsupdate.php`, `nsupdate_ipv4.php`, and
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`nsupdate_ipv6.php` (used by both `index.php` and `nic/update.php`,
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the router/ddclient-facing endpoint) build a shell command string by
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directly interpolating unsanitized `$_GET` input (`hostname`/`myip`/
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`ip`, which become `$host`/`$ip`/`$ipv4`/`$ipv6`) and pass it to
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PHP's `exec()`, which runs it via `/bin/sh -c` — no
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`escapeshellarg()`/`escapeshellcmd()` anywhere. A request like
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`hostname=$(id>/tmp/pwned).dyndns.jayfield.org` would execute
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arbitrary shell commands as `www-data` (the domain-suffix check
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still passes after the `.`-split). `nic/update.php` has no
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application-level auth of its own at all.
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Mitigating factor: the whole `dyndns.jayfield.org` vhost sits behind
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Apache Basic Auth, so this needs valid (or leaked/brute-forced)
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dyndns credentials to reach — not exploitable by an anonymous
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visitor. Compounding factors: PHP is `7.4.33`, EOL since Nov 2022,
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`disable_functions` is empty (`exec` fully available); `index.php`'s
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`pass == '_NO_PASS_'` check is a hardcoded magic string, not real
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per-user auth, so any valid dyndns credential can update *any* of
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the zone's 5 hostnames (`jens`, `kack`, `test`, `uschi`, `vpn`), not
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just its own; and the vhost's access logging turned out to be a
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no-op (shared `access.log` has 0 lines), so past exploitation can't
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be fully ruled out from logs alone — though file mtimes, `www-data`
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processes/crontab, and current zone contents all look unremarkable,
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consistent with unexploited.
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Fix: switch `exec()` to pass the nsupdate command list via
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`proc_open`/`popen` writing to stdin (no shell interpolation of
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user input at all), or at minimum wrap every interpolated value in
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`escapeshellarg()`; add strict `filter_var`/regex validation on the
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hostname label and IP before use. Not yet applied.
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- [x] **Public static site (`jayfield.org`/`www.jayfield.org`) was 401'ing every visitor** — done 2026-07-20
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Found while auditing which services are reachable without credentials:
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a stray `/var/www/html/.htaccess` (`AuthType Basic`, same
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`AuthName "Restricted Content"`/`AuthUserFile /etc/apache2/.htpasswd`
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as the intentional `dyndns.jayfield.org` protection) was silently
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requiring login for the DocumentRoot both `jayfield.org` and
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`www.jayfield.org` share — `/var/www` has `AllowOverride all`, so it
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took effect with no vhost-level directive needed. File was dated
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2025-02-18 (`index.html`/`apache.html` themselves are from 2022) —
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predates every other change in this doc by well over a year, almost
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certainly a forgotten leftover rather than intentional, and
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contradicts `README.md`'s own description of both as a public static
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site.
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Fixed: moved to `/root/removed-configs-backup/htaccess-var-www-html.<timestamp>`
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(recoverable, not deleted — same convention as this file's other
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removed-config backups). No Apache reload needed (`.htaccess` is
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read per-request). Verified both `jayfield.org` and
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`www.jayfield.org` now return `200` with real page content;
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`dyndns.jayfield.org`'s own (intentional, vhost-level) Basic Auth is
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untouched and still returns `401` without credentials.
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- [x] **Lock down the dyndns TSIG key file permissions** — done 2026-07-19
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`/etc/bind/dyndns.jayfield.org.key` was `644` (world-readable), holding
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the shared secret that authenticates dynamic DNS updates for
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`dyndns.jayfield.org` with no IP-based `allow-update` backing it up.
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Fixed: `chmod 640` + `chown root:bind` (owner was already correct),
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matching `rndc.key`'s permissions.
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- [x] **Suppress BIND version disclosure** — done 2026-07-19
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No `version` statement in `named.conf.options`, so
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`dig CH TXT version.bind @ns1.jayfield.org` leaked the exact BIND
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version (`9.18.39`) — a minor fingerprinting aid for attackers.
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Fixed: added `version "unknown";` inside the `options {}` block,
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validated with `named-checkconf`, and applied via `rndc reload`.
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Verified `dig CH TXT version.bind` now returns `"unknown"`.
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- [x] **Add response rate limiting (RRL)** — done 2026-07-19
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No `rate-limit {}` block was configured. Since `allow-query { any; }`
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is required for a public authoritative zone, RRL is the standard
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mitigation against the server being used for spoofed-source DNS
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reflection/amplification against third parties.
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Fixed: added `rate-limit { responses-per-second 10; window 5; }` to
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`named.conf.options`, validated with `named-checkconf`, and applied
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via `rndc reload`. Started with conservative defaults (10/s, 5s
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window) — revisit if legitimate high-volume resolvers get throttled.
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- [x] **Add HSTS headers to all vhosts** — done 2026-07-19
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No vhost sent a `Strict-Transport-Security` header, leaving a window
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for on-path SSL-stripping on a user's very first plaintext request to
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any domain.
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Fixed: added `Header always set Strict-Transport-Security
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"max-age=63072000; includeSubDomains"` to all 6 domain `:443` blocks
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(`dyndns`, `jayfield.org`, `www`, `mail`, `web`, `cloud`) — skipped
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`default-ssl.conf` since it's the self-signed catch-all with no real
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trusted hostname for a browser to pin. Validated with
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`apache2ctl configtest`, applied via `systemctl reload apache2`,
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verified live with `curl -sI` against all 6 domains.
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- [x] **`jayfield.org` had no `:80` vhost of its own** — done 2026-07-19
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Bare `http://jayfield.org` fell through to the `dyndns` default vhost
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and redirected to the wrong domain.
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Fixed: added a `:80` block to `jayfield.org.conf` redirecting to
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`https://jayfield.org/`, matching the `dyndns`/`mail` pattern.
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Verified: `curl -sI http://jayfield.org/` → `302` with
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`Location: https://jayfield.org/`.
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- [x] **SSH: disable root login + password auth** — done 2026-07-19
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`PermitRootLogin yes` and `PasswordAuthentication yes` were both still
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enabled (the "known deviation" flagged in `SETUP.md` §1) — every
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credential-stuffing bot on the internet got a real login prompt to
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grind against.
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Fixed: `PermitRootLogin no`, `PasswordAuthentication no`,
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`PubkeyAuthentication yes` in `/etc/ssh/sshd_config` (backed up as
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`sshd_config.bak.20260719225249`). The `Match Group sftp` block's own
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`PasswordAuthentication yes` was left as-is — separate, already-chrooted,
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no-shell/no-forwarding accounts, not part of this risk. Validated with
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`sshd -t`, applied via `systemctl reload sshd`, verified live with
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`sshd -T` and a fresh key-only connection before considering it done.
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- [x] **Portainer's `:9443` UI is unreachable in HSTS-enforcing browsers** — done 2026-07-20
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`https://alpha.jayfield.org:9443` threw
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`MOZILLA_PKIX_ERROR_SELF_SIGNED_CERT` in Firefox with no click-through
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option ("keine Ausnahme kann hinzugefügt werden"). Root cause: the
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`includeSubDomains` HSTS policy sent by the real `alpha.jayfield.org`
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vhost (`Strict-Transport-Security` header, added in the item above)
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pins the *hostname* to HTTPS-with-a-trusted-cert on every port, but
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Portainer (`README.md` §Docker services) was still serving its stock
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self-signed cert directly on `9443`. Not a MITM — self-inflicted by
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combining HSTS with an unproxied self-signed service.
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Fixed: added a `portainer` A record to `db.jayfield.org` (SOA serial
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`2022032216` → `2022032217`); recreated the `portainer` container
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binding the HTTPS UI to `127.0.0.1:9443:9443` instead of publishing it
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(old container kept renamed until the new one was verified, then
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removed, matching the update procedure documented in `README.md`);
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added an Apache vhost for `portainer.jayfield.org`
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(`ProxyPass`/`ProxyPassReverse` to `https://127.0.0.1:9443/`,
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`SSLProxyEngine on`, `SSLProxyVerify none` + `SSLProxyCheckPeerCN off`/
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`SSLProxyCheckPeerName off` for the loopback hop to Portainer's
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self-signed cert) — same pattern as `web.jayfield.org`/
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`cloud.jayfield.org` (`SETUP.md` §4/§5); issued a real cert via
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`certbot --apache -d portainer.jayfield.org --redirect`; added the
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standard HSTS header. Left the `8000` edge-agent tunnel port
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published as-is — no evidence it's in use.
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Verified: `openssl s_client`/`curl` confirm the Let's Encrypt cert
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(not self-signed) and `Strict-Transport-Security` header on
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`https://portainer.jayfield.org`, `http://` redirects 301 to
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`https://`, and `ss -ltnp` shows `9443` bound to `127.0.0.1` only
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(via `docker-proxy`), so it's no longer reachable on the public
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interface at all — access is now exclusively via
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`https://portainer.jayfield.org`.
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One transient wrinkle during rollout: the very first few requests
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through the new proxy vhost returned a stray `401` with dyndns's
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Basic Auth realm ("Restricted Content") — looked alarming, but
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`LogLevel trace8` on the vhost showed Apache correctly SNI-matching
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and proxying to the new container with a clean backend `200`;
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resolved itself within seconds (looked like a stale pooled proxy
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connection surviving the container recreate) and was stable across
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repeated checks before the debug logging was removed again.
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- [x] **fail2ban: `sshd` jail was evadable via low-and-slow attempts** — done 2026-07-19
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Default `findtime=30m`/`maxretry=3` never triggered for `47.76.192.176`,
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which had been hitting `root`/`jayfield` logins roughly every 33 minutes
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for most of a day — just outside the 30-minute window, so failures kept
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aging out before reaching 3 strikes. Confirmed via `fail2ban.log`
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(`Found`/`Ban` counts) that no other jail showed the same per-IP timing
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pattern; a separate, *distributed* single-shot scan on `apache-noscript`
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was noted but left open (see `README.md`).
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Fixed: `/etc/fail2ban/jail.d/sshd-findtime.local` overrides `sshd` to
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`findtime=1d`, `maxretry=4`, `bantime=1d`, kept in its own drop-in
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rather than editing the Debian-packaged jail file. Applied via
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`fail2ban-client reload sshd`; `47.76.192.176` was banned on its very
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next attempt after the change.
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