#+title: gitbay threat model

What the forge trusts, what it refuses to do, and where the boundaries
are. This is the reference for security review; it complements the audit
log and hardening notes in [[Admin]]. Diagrams, data flows, a controls
matrix and the open gaps are in the [[file:Architecture/00-Overview.org][Architecture]] pages.

* What gitbay never does

- *Execute repository content.* Git object contents are never run. Hooks
  are gitbay's own binary, invoked by git; they compute facts and ask the
  daemon over a unix socket. Repo files are only ever read.
- *Hold a signing key.* There is no server-side signing key. "Verified"
  means a signature made by a key the *user* registered — the server
  never vouches for a commit it did not receive already signed. Merge
  commits the server creates are honestly =unsigned=.
- *Serve repository HTML on its own origin as active content.* Raw file
  serving is =text/plain= with =nosniff=. Rendered markdown/org is
  sanitized (bluemonday) and served under a CSP that forbids scripts.
- *Put secrets in argv, URLs, or logs, with one documented exception.*
  Import and mirror credentials, registration invites, and API tokens
  travel on stdin or in request bodies, never as command arguments
  (visible in =/proc=) or query strings. The one exception is the
  emailed login link, =/login?token=...=: single-use, 15-minute expiry,
  and the response that consumes it carries =Cache-Control: no-store= so
  no intermediary keeps a copy. An operator running gitbay behind a
  reverse proxy should configure that proxy to strip the query string
  from its own access logs. Tokens are stored only as SHA-256 hashes.
- *Name a mail recipient in the log.* A queued mail is logged by its
  queue row id, never by address, and the relay's own error is redacted
  before it is logged because a rejection usually quotes the address it
  rejected. The unredacted error and the address stay on the row, which
  an instance admin reads on =/admin=: the database holds who, the log
  holds which. One rule for every mail type — notifications, dependency
  reports and login links all drain the same queue (krz/gitbay#173).
- *Confirm the existence of private repositories.* Every surface answers
  "not found" identically for a private repo and a nonexistent one — web
  pages, git transport, control commands, release asset downloads.

* Trust boundaries

- *SSH public key = identity.* The SSH username is ignored; the presented
  key's fingerprint resolves to an account. Key uniqueness is global.
- *Revocation is immediate.* Every exec and every git transport session
  re-reads its key. Removing a key, removing a deploy key, disabling or
  deleting an account closes the connections the affected keys opened:
  a git transport is killed with its children, and a push killed before
  its pre-receive hook answers moves no ref. A control command already
  inside its database write finishes it; its output is lost. A
  revocation made by =gitbayd admin= on the host, another process, is
  found within 15 seconds. In =ssh.mode = "system"= each exec is its
  own process: the next exec is refused, one already running is not cut.
- *Per-instance trust.* Email verification and key registration are local
  to an instance and never transfer. Account migration re-registers keys
  and re-verifies emails on the target by design.
- *The control plane is one command registry*, fully usable from stock
  OpenSSH and fronted unchanged by the JSON API and the web. No command
  belongs to one surface (#234): what a caller may do is the account's
  rights narrowed by its credential's scope, decided in one place, so a
  bearer token is worth exactly its scope and no more, and a token or
  SSH key with an expiry cannot create a credential that outlives it.
  Browser sessions are not covered yet (#297). Git transport never runs
  over the API.
- *Anonymous surfaces* — HTTPS clone of public repos, =git://= where
  enabled, the read-only web UI — carry no credentials and expose only
  public data. HTTP push is refused via a pkt-line =ERR=, never a 401.

* Attacker-controlled parsers

Every parser that eats bytes from a pusher, a key registrant, or an
anonymous client has a fuzz target and must never panic:

- =internal/protocol= — the SSH command tokenizer (fuzzed against argv
  round-tripping).
- =internal/gitd= — the =git://= pkt-line reader.
- =internal/sig= — the commit parser, the SSHSIG armor decoder and blob
  parser, and the OpenPGP armored-key reader.

Run =deploy/audit.sh= to exercise them plus =go vet= and =govulncheck=.

* Secret handling

Tokens (web sessions, login links, email verification, API bearer tokens,
deploy/CI) are random 256-bit values. Only their SHA-256 hash is stored,
and verification is a database index lookup on that hash — the secret
itself is never compared in Go, so there is no timing oracle to exploit.
Webhook payloads are signed outbound with HMAC-SHA256; the forge verifies
no inbound HMAC.

* Network-facing request forgery

Webhook delivery, GitHub-history import =--api-base= and mirror
remotes, which make the *server* open an outbound connection to a
user-supplied address, pass the same SSRF guard: the scheme
must be http/https and, unless =webhooks.allow_local= is set, the
resolved address must not be loopback, private, shared
(100.64.0.0/10), link-local, or multicast. The webhook dialer re-checks
at connect time, and the mirror worker resolves and checks before each
sync and pins git to the checked addresses, so a DNS answer that
changes after validation still cannot reach private space. Redirects
are never followed. =repo import --from= is the exception: its clone
checks the scheme but not the address, and follows git's default
redirect rule (#298).

* Rendering pushed markup

Rendered markup is attacker-controlled: a README, a wiki page and a
profile's about text are all whatever someone pushed or typed. The risk
is not only what the output contains but what the *parser* is willing to
go and fetch — the filesystem counterpart of the SSRF guard above.

Org is rendered by go-org, whose default configuration resolves
=#+INCLUDE:= and =#+SETUPFILE:= targets with =os.ReadFile=. Both are
refused outright (=orgConfig()= in =internal/httpd=): the file is never
opened and the keyword stays the inert text it already was, so the rest
of the document renders normally. There is no safe subset to allow
instead — an absolute path skips go-org's relative-path join, a relative
one resolves against the daemon's working directory, and the content
came from a git object rather than a checkout, so there is no directory
to scope a read to. Markdown is goldmark, which has no include
mechanism. go-org's parse warnings are discarded rather than logged, so
pushed content cannot write to the server's log.

Org output is then sanitized (bluemonday UGC policy) because go-org
passes raw HTML through — export blocks and inline export snippets —
while goldmark drops it and needs no pass. The policy admits chroma's
short token classes and nothing else.

* Web responses

Every response carries =Content-Security-Policy= (no scripts, no plugins,
no embedding; inline styles allowed for chroma and label chips; images
from any origin so external README images render), =X-Frame-Options:
DENY=, =X-Content-Type-Options: nosniff=, =Referrer-Policy: no-referrer=,
and =Strict-Transport-Security= when TLS is on. The UI needs no
JavaScript, so =script-src 'none'= costs nothing.

* The CI runner

=gitbay-runner= is the one component that executes repository content.
gitbayd never does: it reads =.gitbay/ci.yml= and queues a build, and a
runner, polling over SSH, clones the commit and runs its steps.

- *What the runner holds.* A key of scope =runner=, which the dispatcher
  confines to =runner next=, =runner log= and =runner done= and to
  read-only git, and which claims, logs and finishes builds only for
  the repositories it is attached to (=repo runner add=). A step that
  reads the key off the disk gets exactly that: it cannot administer
  the instance, push, read a repository the runner's account cannot, or
  touch another repository's builds. An admin key still works for the
  runner protocol so an operator can rotate at their own pace; a runner
  host should not hold one. Untrusted builds are skipped unless the
  runner asks with =-untrusted=, so a runner on a user's machine never
  executes a stranger's branch by default.
- *What a build sees.* The commit, the =GITBAY_*= variables and the
  repository's secrets — unless the head came from another repository.
  A merge request from a fork is built in the target as untrusted, with
  no secrets, so a stranger's branch cannot read the target's deploy
  credentials. The step environment is *constructed*, not inherited: a
  build gets =PATH=, =HOME=, =LANG=, =CI=, its own variables and its
  secrets, and nothing the operator set on the service. =HOME= is a build
  home under the runner's =-workdir=, not the runner's own home, so a
  build cannot read the =.netrc=, =.npmrc= or =.gitconfig= where tools
  keep credentials. A trusted build's home belongs to its repository
  and persists, so caches survive; an untrusted build's home is new,
  empty and removed when the build ends, so nothing a fork's build
  writes is read by a later build (krz/gitbay#255). The claim names a
  build's trust explicitly, and a runner that finds no trust flag treats
  the build as untrusted.
- *Where it runs.* Steps run in a rootless podman container, one per
  job, with the workspace bind mounted and nothing else. The clone
  happens outside it with the runner's key, so the container never sees
  =GIT_SSH_COMMAND=, the key, or the runner's environment. =-isolation
  none= runs steps on the host as before, for an instance where every
  repository is trusted; there is no automatic fallback to it — a runner
  configured for podman that cannot find one refuses to start, because
  dropping isolation silently is worse than a stopped runner. The
  systemd drop-in still adds =ProtectSystem=full= and the cgroup
  protections, and =-repos= still limits a runner to named
  repositories. =ProtectKernelTunables= is *off*: it overmounts =/proc=
  in the unit's namespace and the kernel then refuses a proc mount in
  any child user namespace, which every rootless container needs; the
  container masks the same paths for the build itself.
  =NoNewPrivileges= is *off*: rootless podman sets up its
  namespace with the setuid =newuidmap=, which that flag blocks, so the
  choice is between it and containers at all. Containers are the stronger
  boundary — the flag constrained a process that was already running
  arbitrary repository code, and under podman that code no longer runs in
  the runner's process context. Under =-isolation none= there is no
  container and the flag should be on.
- *Images are provisioned by the operator, not fetched by a build.* The
  runner passes =--pull=never=, so =image:= chooses among what the host
  already has rather than naming anything on the internet. On an
  instance with open registration that is the difference between a
  curated set and arbitrary code from a registry nobody vetted.
- *What a build can reach.* Outbound internet, trusted or not: a fork's
  merge request to a Go repository has to fetch its modules. On the
  runner's host, the rules below limit it to the forge's public ports
  22, 80 and 443. Under pasta a build's container holds the host's own
  public address, and pasta translates =169.254.1.2= (its
  =--map-guest-addr=) to that address. A runner that polls the daemon
  over loopback starts its containers with =--network
  pasta:--no-map-gw=, which is podman's default stated explicitly, and
  gives them =GITBAY_SSH= at =169.254.1.2=, with the forge's port when
  it is not 22. The runner's source address is =127.0.0.1=. An nftables
  table (=deploy/gitbay-runner-egress.nft=) rejects every connection
  the runner's user makes to the host's own addresses except
  =127.0.0.1:22=, DNS on loopback, and 22, 80 and 443 on the public
  address: the operator's sshd on 2222 and anything bound to loopback
  are closed to it. Under rootless podman a build's connections are
  made by pasta as the runner's user, so the table cannot tell a build
  from its runner and leaves =127.0.0.1:22= open; that no build reaches
  the host's loopback is measured from inside a build by runbook R3.
  The runner does not start without the table. The SSH auth limiter
  counts failures per source address and, once an address is over the
  limit, refuses every key from it until the window passes, the
  runner's included; with registration open or by invite an unknown
  key never counts (krz/gitbay#260). Under =-isolation none= a build
  runs on the host and shares its loopback; the table still applies,
  since it runs as the same user.

Under =-isolation none=, anything a step can do as the runner's user a
pushed =ci.yml= can do. Under podman a step is confined to its
container, the bind-mounted workspace and its build home: a trusted
build's cache is read only by later trusted builds of the same
repository, and an untrusted build's home is discarded with it. Treat
the runner host as executing untrusted code all the same: keep it off
the daemon's host where the database lives, or scope it to repositories
whose writers you trust. gitbay.org does the latter — its runner builds
only the repositories the operator names.

* What has not been audited

The 2026-09 sweep (krz/gitbay#149) read this repository against the
claims above. Its two findings — review verdicts from accounts without
write access deciding merge gates (#147), and control commands having no
write rate limit while the API had one (#148) — are fixed, as is #173,
found afterwards in the same milestone. What it did not reach, and why,
is recorded here rather than in a closed issue:

- *The host.* systemd sandboxing, sshd on 2222, the firewall,
  unattended-upgrades, fail2ban, disk and file modes, restic append-only
  credentials. Reading production configuration is a separate exercise
  from auditing the source, and needs doing against bay1.
- *The supply chain beyond =govulncheck=.* No review of what the
  dependency set is, who maintains it, or what a compromised release of
  any of it would reach.
- *The runner host as an execution environment.* Nobody has tried to
  escape what is there. #144 covers the missing isolation.
- *Timing and traffic analysis.* Token comparison is a hash index lookup
  by design, but nothing has been measured.
- *Denial of service by resource exhaustion* beyond rate: large pushes,
  pathological diffs, deep histories, zip bombs in LFS.

A sweep is a point in time. This section says what a reader should not
assume has been checked.

* Residual risks, accepted

- External images in rendered READMEs and profile about text load from
  their origin (no image proxy), which the author can use as a tracking
  pixel against a viewer. A profile is the wider surface of the two: it
  is linked from every commit and issue its owner touches. Documented;
  proxying is future work.
- Backups snapshot the database first, and repository deletes and
  moves wait out a full backup. Each repository's refs are archived
  before its objects, so every archived ref finds the objects it
  reaches, unless git's own automatic gc after a push repacks during
  the walk: the archive can then miss objects, and =--verify= reports
  it. A push during a backup may be missing from the archive, or
  present as objects no archived ref names, and a repository's refs may
  be newer than the database snapshot (see [[Admin]]).
- The audit log lives in the database the daemon writes, so anyone with
  the daemon user's access can change it. The hash chain makes an edited
  or removed row show as a break under =gitbayd admin audit verify=,
  except at the end: removing the newest rows, and writing new rows
  under their freed ids, leaves a valid chain. Only comparing verify's
  last id and hash with the daemon's journal copy shows it, and rows
  written outside the daemon (=gitbayd shell= under =ssh.mode =
  "system"=, host =gitbayd admin= commands) have no journal copy.
- A global signature-verification epoch over-invalidates the cache on any
  trust-input change. Correct, not a leak; a performance tradeoff.
- A build's secrets are environment variables inside its container, so
  they are visible to =podman inspect= as the runner's user — the same
  user that already holds them in memory. They reach podman through a
  0600 env file rather than argv, since =/proc= is world-readable. A
  value with a newline in it — a private key — cannot go in that file;
  it is named on podman's command line with =--env NAME= and valued in
  the runner-owned podman process's environment, so it never touches
  argv either.