If you discover a security issue with bibcheck, please report it via:

• A private GitHub Security Advisory at https://github.com/de-otio/bibcheck/security/advisories
• Or email: richard.myers@de-otio.org

We aim to acknowledge reports within 7 days.

bibcheck collects no telemetry. The only outbound personal data is the polite-pool email address (when configured via [apis] crossref_mailto / openalex_mailto), which is sent to api.crossref.org and api.openalex.org as a User-Agent string and ?mailto= query parameter. Setting these fields is optional.

bibcheck queries the following public APIs as part of its operation:

• CrossRef (api.crossref.org) — DOI metadata
• OpenAlex (api.openalex.org) — bibliographic metadata
• OpenLibrary (openlibrary.org) — ISBN metadata

bibcheck performs HEAD requests against URLs in your bibliography for canonical-edition verification. The SSRF mitigation has several layers:

• Input-host allowlisting before any request. The hostname of each bibliography URL is checked against the trusted-host whitelist configured in [trusted_hosts] before any network request is dispatched. A URL whose host is not allowlisted (for example a cloud metadata endpoint such as 169.254.169.254) is reported as wrong-host and is never fetched.
• Per-hop private-IP rejection. Every hop — the initial URL and every redirect target, regardless of whether the redirect stays on the same host — is validated. Literal-IP hosts are classified directly; DNS names are resolved and every returned address is checked. A hop is rejected if it targets a private or non-routable address: IPv4 loopback (127.0.0.0/8), RFC 1918 (10/8, 172.16/12, 192.168/16), link-local (169.254.0.0/16), the "this host" range (0.0.0.0/8), CGNAT shared space (100.64.0.0/10), IPv6 loopback (::1), ULA (fc00::/7), IPv6 link-local (fe80::/10), and IPv4-mapped IPv6 forms (e.g. ::ffff:127.0.0.1). Non-dotted IPv4 literals in decimal, octal, or hex form (e.g. http://2130706433/, http://0x7f000001/) are normalized and classified too.
• Scheme restriction. Only http/https URLs are accepted at any hop; file:, data:, ftp:, and other schemes are rejected.
• Final-destination allowlisting. After redirects are followed, the final destination host is re-checked against the trusted-host whitelist.

Limitation: the private-IP check resolves DNS and validates the returned addresses, but the subsequent connection performs its own resolution, so a DNS-rebinding attacker who flips a record between the two lookups is not fully mitigated (TOCTOU). Closing this window requires pinning the validated IP into the connection (a custom dispatcher) and is not yet implemented.

User-supplied phrase-denylist regex patterns are compiled with re2js for linear-time guarantees (ReDoS mitigation).