kev

A Crystal implementation of the CISA Known Exploited Vulnerabilities (KEV) catalog — parsing, querying, fetching, and JSON serialization for the official feed.

• Strict, schema-bound parser modeled on the official KEV JSON schema — validates cveID/CWE patterns at parse time
• Type-safe Vulnerability and Catalog models
• Chainable Query builder for vendor / product / CWE / ransomware / due-date filters
• Built-in HTTP Client with ETag / If-Modified-Since support, optional redirect-following, and URL-rich error messages
• Lossless JSON round-trips against the canonical CISA feed — including unknown-but-valid knownRansomwareCampaignUse strings preserved on known_ransomware_campaign_use_raw
• CSV mirror support via Catalog.parse_csv / Client.fetch_csv and CSV export via Catalog#to_csv
• Explicit validate! / valid? for re-running schema checks on programmatically constructed records
• Convenience surface: Catalog#search, #diff, #stats, #group_by_*, #latest / #oldest, and per-entry deep links (#cisa_url / #nvd_url / #mitre_url)

Installation

Add the dependency to your shard.yml:

dependencies:
  kev:
    github: hahwul/kev.cr

Then shards install.

Usage

Parse a catalog

require "kev"

catalog = KEV.parse(File.read("known_exploited_vulnerabilities.json"))
catalog.size                              # => 1592
catalog.catalog_version                   # => "2026.05.15"
catalog["CVE-2021-44228"].vendor_project  # => "Apache"

Fetch the live CISA feed

catalog = KEV.fetch
puts "#{catalog.size} entries, released #{catalog.date_released}"

# Long-lived client with conditional GETs:
client = KEV::Client.new
first = client.fetch
later = client.fetch_if_modified  # => nil when the feed is unchanged

# CSV mirror — same per-row data, no catalog metadata:
csv_catalog = KEV::Client.fetch_csv

# Follow redirects (off by default — set when pointing at a mirror):
KEV::Client.new(url: "https://example.com/kev.json", max_redirects: 3).fetch

Snapshot diff and summary

old = KEV::Catalog.parse(File.read("kev-yesterday.json"))
new = KEV.fetch

delta = old.diff(new)
delta.added.each   { |v| puts "added: #{v.summary}" }
delta.removed.each { |v| puts "removed: #{v.cve_id}" }
delta.changed.each { |before, after| puts "edited: #{after.cve_id}" }

# One-call rollup — totals, ransomware, overdue, top vendors / CWEs / years.
puts new.stats(top: 5)
# => #<KEV::Stats total=1592 ransomware=321 overdue=1590 years=12 top_vendor=Microsoft(371)>

Search and group

catalog.search("log4j")          # substring across cve_id, name, description, vendor, product
catalog.latest(10)               # newest first
catalog.oldest(5)                # earliest first
catalog.group_by_year[2024]      # all 2024-numbered CVEs
catalog.group_by_vendor["Microsoft"]
catalog.group_by_cwe["CWE-79"]
catalog.group_by_ransomware[KEV::RansomwareUse::Known]

Per-entry deep links

v = catalog["CVE-2021-44228"]
v.cisa_url   # CISA catalog page filtered to this CVE
v.nvd_url    # NVD detail page
v.mitre_url  # MITRE CVE record
v.summary    # one-line digest with [ransomware]/[overdue] flags

Export to CSV

File.write("kev.csv", catalog.to_csv)
KEV::Catalog.parse_csv(File.read("kev.csv"))  # round-trips

Validate programmatic records

from_json enforces every schema-level constraint, but constructor and in-place edits bypass that path. validate! / valid? re-run the schema checks on demand:

catalog.validate!         # raises KEV::InvalidValueError on the first bad entry
catalog.valid?            # => true / false

vuln.validate!            # same, scoped to one entry

Look up and filter

catalog.find("CVE-2021-44228")          # => KEV::Vulnerability | nil
catalog["CVE-2021-44228"]               # => raises KeyError on miss
catalog["CVE-2021-44228"]?              # => same as find

catalog.by_vendor("Microsoft")          # case-insensitive
catalog.by_cwe("CWE-79")                # or just "79"
catalog.ransomware                      # Array(Vulnerability)
catalog.overdue                         # past their due date
catalog.due_within(30.days)

Chainable queries

catalog.query
  .vendor("Microsoft")
  .ransomware
  .added_on_or_after(Time.utc(2024, 1, 1))
  .sort_by_due_date
  .to_a

Other Query filters: product, name_matches, description_matches, cwe, non_ransomware, year, due_on_or_after, due_on_or_before, overdue, due_within, and a generic where { |v| ... } escape hatch.

Vulnerability predicates

v = catalog["CVE-2021-44228"]
v.known_ransomware?            # => true
v.overdue?                     # => true (relative to now)
v.days_until_due               # => negative when overdue
v.remediation_window_days      # => 14
v.has_cwe?("CWE-917")          # => true
v.cve_year                     # => 2021

Equality, ordering, sets

Vulnerability equality is keyed by cve_id, so deduping across feed snapshots is straightforward:

seen = Set(KEV::Vulnerability).new
catalog.each { |v| seen << v }

Vectors sort by date_added (with cve_id as a stable tiebreak), and Catalog is Enumerable + Indexable, so all the usual collection methods work directly.

JSON serialization

Vulnerability#to_json and Catalog#to_json emit output that matches the canonical CISA feed shape — field names and order are preserved, and the result round-trips through KEV::Catalog.parse. Empty optional strings (notes: "") and unknown-but-valid knownRansomwareCampaignUse values are preserved verbatim so byte-level diffs against the upstream feed do not show spurious deltas.

require "json"

catalog = KEV.parse(File.read("kev.json"))
File.write("kev_filtered.json", catalog.query.ransomware.to_a.to_json)

reparsed = KEV::Catalog.parse(catalog.to_json)
reparsed.size == catalog.size  # => true

Errors

All exceptions inherit from KEV::Error:

• KEV::ParseError — malformed JSON, missing fields, bad dates.
• KEV::MissingFieldError < ParseError — a schema-required field is absent.
• KEV::InvalidValueError < ParseError — a field value violates a schema-level pattern (e.g. a malformed cveID or a CWE that does not match ^CWE-[0-9]+$).
• KEV::FetchError — transport-level failures in KEV::Client.

KEV.parse? and KEV::Catalog.parse? return nil instead of raising.

Development

crystal spec

License

MIT. See LICENSE.

The KEV catalog itself is published by the U.S. Cybersecurity and Infrastructure Security Agency (CISA) and is in the public domain.

Contributors

• hahwul — creator and maintainer