{"id":"CVE-2026-47067","aliases":["EEF-CVE-2026-47067","EUVD-2026-31691","GHSA-9653-rcfr-5c62"],"status":"published","title":"Atom table exhaustion via unrecognized URL schemes in hackney","description":"Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. The URL parser in src/hackney_url.erl converts every unrecognized URL scheme to a permanent BEAM atom via binary_to_atom/2. BEAM atoms are never garbage-collected and the atom table defaults to a hard limit of 1,048,576 entries. An attacker who can supply URLs with attacker-chosen scheme prefixes — directly as request targets, as configured webhook URLs, or via Location headers followed during redirects — can exhaust the atom table and crash the entire BEAM VM with system_limit.\n\nThis issue affects hackney: from 2.0.0 before 4.0.1.","severity":{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00753,"percentile":0.554,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-770"],"published":"2026-05-25T14:00:48Z","modified":"2026-10-28T02:30:32Z","fixes":[{"ecosystem":"Hex","package":"hackney","fixed_in":["4.0.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Hex","package":"hackney","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0"},{"fixed":"4.0.1"}]}]},{"source":"osv","ecosystem":"Hex","package":"hackney","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"4.0.1"}]}],"versions":["2.0.0","2.0.1","3.0.0","3.0.1","3.0.2","3.0.3","3.1.0","3.1.1","3.1.2","3.2.0","3.2.1","4.0.0"]},{"source":"osv","ecosystem":"Hex","package":"hackney","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"4.0.1"}]}],"versions":["2.0.0","2.0.1","3.0.0","3.0.1","3.0.2","3.0.3","3.1.0","3.1.1","3.1.2","3.2.0","3.2.1","4.0.0"]}],"products":[{"vendor":"benoitc","product":"hackney"},{"vendor":"hackney","product":"hackney"}],"references":[{"url":"https://github.com/benoitc/hackney/security/advisories/GHSA-9653-rcfr-5c62","tags":["vendor-advisory","related","exploit","Exploit","Patch","Vendor Advisory","advisory","web"]},{"url":"https://cna.erlef.org/cves/CVE-2026-47067.html","tags":["related","Patch","Third Party Advisory","web"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-47067","tags":["related","Patch","Third Party Advisory","web"]},{"url":"https://github.com/benoitc/hackney/commit/31f6f0e27e096ad88743dfded4f030a3ee74972e","tags":["patch","Patch","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47067","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-9653-rcfr-5c62"},{"url":"https://github.com","tags":["web"]},{"url":"https://repo.hex.pm","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47067.json","tags":["advisory"]},{"url":"https://github.com/benoitc/hackney","tags":["package"]},{"url":"https://hex.pm/packages/hackney","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-47067","title":"Atom table exhaustion via unrecognized URL schemes in hackney","description":"Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. The URL parser in src/hackney_url.erl converts every unrecognized URL scheme to a permanent BEAM atom via binary_to_atom/2. BEAM atoms are never garbage-collected and the atom table defaults to a hard limit of 1,048,576 entries. An attacker who can supply URLs with attacker-chosen scheme prefixes — directly as request targets, as configured webhook URLs, or via Location headers followed during redirects — can exhaust the atom table and crash the entire BEAM VM with system_limit.\n\nThis issue affects hackney: from 2.0.0 before 4.0.1.","status":"published","published":"2026-05-25T14:00:48.507Z","modified":"2026-05-27T15:41:27.821Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","level":"high","assessor":"cna"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T13:36:51.6229Z"}],"euvd":[{"id":"EUVD-2026-31691","description":"Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. The URL parser in src/hackney_url.erl converts every unrecognized URL scheme to a permanent BEAM atom via binary_to_atom/2. BEAM atoms are never garbage-collected and the atom table defaults to a hard limit of 1,048,576 entries. An attacker who can supply URLs with attacker-chosen scheme prefixes — directly as request targets, as configured webhook URLs, or via Location headers followed during redirects — can exhaust the atom table and crash the entire BEAM VM with system_limit.\n\nThis issue affects hackney: from 2.0.0 before 4.0.1.","status":"published","published":"2026-05-25T14:00:48Z","modified":"2026-05-27T15:41:27Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","level":"high"}],"updated_at":"2026-11-02T18:21:03.926243Z"}],"ghsa":[{"id":"GHSA-9653-rcfr-5c62","title":"Hackney vulnerable to atom-table exhaustion via unrecognized URL schemes","description":"### Summary\n\n[CVE-2026-47067](https://nvd.nist.gov/vuln/detail/CVE-2026-47067) is an atom table exhaustion vulnerability (CWE-770) in hackney's URL parser (`src/hackney_url.erl`). `hackney_url:parse_url/1` converts every URL scheme it encounters into a BEAM atom via `binary_to_atom/2`. Because BEAM atoms are never garbage-collected and the atom table has a hard limit of 1,048,576 entries, an attacker who can feed URLs with attacker-chosen scheme prefixes — directly as request targets, as webhook/callback URLs, or via `Location` headers in redirect chains — can exhaust the atom table and crash the entire BEAM VM with `system_limit`.\n\n### Details\n\n**1. Scheme extraction and conversion**\n\nIn `src/hackney_url.erl`, `parse_url/1` extracts the scheme binary (the part before `://`), validates it with `is_valid_scheme/1` (RFC 3986 alphabet: alpha-led, `\u003c=19` bytes, alphanumeric/`+`/`-`/`.` body), lowercases it, then calls:\n\n```erlang\nbinary_to_atom(SchemeLower, utf8)\n```\n\nThe resulting atom is stored on the `#hackney_url{}` record and returned to the caller.\n\n**2. Permanent atom accumulation**\n\nThe validation constrains the alphabet but not uniqueness. The allowed scheme space is enormous (≈52·65¹⁸ values), far exceeding the default atom limit of 1,048,576. Each distinct scheme mints a new permanent atom. Even when hackney subsequently rejects an unsupported scheme with `{error, {unsupported_scheme, _}}`, the atom has already been interned and is never reclaimed.\n\n**3. Crash vector**\n\nThe most dangerous path is redirect following: when hackney follows a `Location` header, the redirect target URL is re-parsed by the same function. An attacker-controlled server can serve a sequence of redirects — or a batch of URLs from an upstream feed — each with a fresh unique scheme, driving the atom count monotonically upward. At the limit the BEAM emits `system_limit` and the node terminates; recovery requires a full restart.\n\n### PoC\n\n1. Call `hackney_url:parse_url/1` (or `:hackney.request/5`) repeatedly with URLs whose scheme prefixes are unique on each call: `aaaa://x`, `aaab://x`, `aaac://x`, …\n2. After enough iterations, observe `erlang:system_info(:atom_count)` climbing by one per unique scheme.\n3. At 1,048,576 atoms the VM crashes with `system_limit`.\n\nAlternatively, point hackney at a server that replies with a feed of ~1M URLs with distinct schemes (or uses redirect chains with rotating schemes); the atom table is exhausted and the node crashes without the client being able to intervene.\n\n### Impact\n\nUnauthenticated remote denial of service via permanent resource exhaustion leading to VM termination. Any application using hackney 2.0.0 through 4.0.0 that processes attacker-influenced URLs — direct request targets, webhook URLs, or `Location` headers in followed redirects — is affected. No authentication or special configuration is required. CVSS v4.0 score: **8.7 (HIGH)**.\n\n## References\n\n* Introduction commit: https://github.com/benoitc/hackney/commit/d9713695c0d99855d12c73fd8a0b4be0543950c4\n* Patch commit: https://github.com/benoitc/hackney/commit/31f6f0e27e096ad88743dfded4f030a3ee74972e","status":"published","published":"2026-06-26T22:01:36Z","modified":"2026-06-26T22:01:37Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:40:34.713036Z"}],"nvd":[{"id":"CVE-2026-47067","description":"Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. The URL parser in src/hackney_url.erl converts every unrecognized URL scheme to a permanent BEAM atom via binary_to_atom/2. BEAM atoms are never garbage-collected and the atom table defaults to a hard limit of 1,048,576 entries. An attacker who can supply URLs with attacker-chosen scheme prefixes — directly as request targets, as configured webhook URLs, or via Location headers followed during redirects — can exhaust the atom table and crash the entire BEAM VM with system_limit.\n\nThis issue affects hackney: from 2.0.0 before 4.0.1.","status":"published","published":"2026-05-25T15:16:21.74Z","modified":"2026-07-24T10:10:00.197Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"primary"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:12:20.131508Z"}],"osv":[{"id":"CVE-2026-47067","title":"Atom table exhaustion via unrecognized URL schemes in hackney","description":"Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. The URL parser in src/hackney_url.erl converts every unrecognized URL scheme to a permanent BEAM atom via binary_to_atom/2. BEAM atoms are never garbage-collected and the atom table defaults to a hard limit of 1,048,576 entries. An attacker who can supply URLs with attacker-chosen scheme prefixes — directly as request targets, as configured webhook URLs, or via Location headers followed during redirects — can exhaust the atom table and crash the entire BEAM VM with system_limit.\n\nThis issue affects hackney: from 2.0.0 before 4.0.1.","status":"published","published":"2026-05-25T14:00:48.507Z","modified":"2026-10-28T02:30:32.965199139Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:45:06.231145Z"},{"id":"EEF-CVE-2026-47067","title":"Atom table exhaustion via unrecognized URL schemes in hackney","description":"## Summary\n\nAllocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. The URL parser in src/hackney\\_url.erl converts every unrecognized URL scheme to a permanent BEAM atom via binary\\_to\\_atom/2. BEAM atoms are never garbage-collected and the atom table defaults to a hard limit of 1,048,576 entries. An attacker who can supply URLs with attacker-chosen scheme prefixes — directly as request targets, as configured webhook URLs, or via Location headers followed during redirects — can exhaust the atom table and crash the entire BEAM VM with system\\_limit.\n\nThis issue affects hackney: from 2.0.0 before 4.0.1.","status":"published","published":"2026-05-25T14:00:48.507Z","modified":"2026-07-30T18:22:00.533414Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:46:33.047032Z"},{"id":"GHSA-9653-rcfr-5c62","title":"Hackney vulnerable to atom-table exhaustion via unrecognized URL schemes","description":"### Summary\n\n[CVE-2026-47067](https://nvd.nist.gov/vuln/detail/CVE-2026-47067) is an atom table exhaustion vulnerability (CWE-770) in hackney's URL parser (`src/hackney_url.erl`). `hackney_url:parse_url/1` converts every URL scheme it encounters into a BEAM atom via `binary_to_atom/2`. Because BEAM atoms are never garbage-collected and the atom table has a hard limit of 1,048,576 entries, an attacker who can feed URLs with attacker-chosen scheme prefixes — directly as request targets, as webhook/callback URLs, or via `Location` headers in redirect chains — can exhaust the atom table and crash the entire BEAM VM with `system_limit`.\n\n### Details\n\n**1. Scheme extraction and conversion**\n\nIn `src/hackney_url.erl`, `parse_url/1` extracts the scheme binary (the part before `://`), validates it with `is_valid_scheme/1` (RFC 3986 alphabet: alpha-led, `\u003c=19` bytes, alphanumeric/`+`/`-`/`.` body), lowercases it, then calls:\n\n```erlang\nbinary_to_atom(SchemeLower, utf8)\n```\n\nThe resulting atom is stored on the `#hackney_url{}` record and returned to the caller.\n\n**2. Permanent atom accumulation**\n\nThe validation constrains the alphabet but not uniqueness. The allowed scheme space is enormous (≈52·65¹⁸ values), far exceeding the default atom limit of 1,048,576. Each distinct scheme mints a new permanent atom. Even when hackney subsequently rejects an unsupported scheme with `{error, {unsupported_scheme, _}}`, the atom has already been interned and is never reclaimed.\n\n**3. Crash vector**\n\nThe most dangerous path is redirect following: when hackney follows a `Location` header, the redirect target URL is re-parsed by the same function. An attacker-controlled server can serve a sequence of redirects — or a batch of URLs from an upstream feed — each with a fresh unique scheme, driving the atom count monotonically upward. At the limit the BEAM emits `system_limit` and the node terminates; recovery requires a full restart.\n\n### PoC\n\n1. Call `hackney_url:parse_url/1` (or `:hackney.request/5`) repeatedly with URLs whose scheme prefixes are unique on each call: `aaaa://x`, `aaab://x`, `aaac://x`, …\n2. After enough iterations, observe `erlang:system_info(:atom_count)` climbing by one per unique scheme.\n3. At 1,048,576 atoms the VM crashes with `system_limit`.\n\nAlternatively, point hackney at a server that replies with a feed of ~1M URLs with distinct schemes (or uses redirect chains with rotating schemes); the atom table is exhausted and the node crashes without the client being able to intervene.\n\n### Impact\n\nUnauthenticated remote denial of service via permanent resource exhaustion leading to VM termination. Any application using hackney 2.0.0 through 4.0.0 that processes attacker-influenced URLs — direct request targets, webhook URLs, or `Location` headers in followed redirects — is affected. No authentication or special configuration is required. CVSS v4.0 score: **8.7 (HIGH)**.\n\n## References\n\n* Introduction commit: https://github.com/benoitc/hackney/commit/d9713695c0d99855d12c73fd8a0b4be0543950c4\n* Patch commit: https://github.com/benoitc/hackney/commit/31f6f0e27e096ad88743dfded4f030a3ee74972e","status":"published","published":"2026-06-26T22:01:36Z","modified":"2026-06-26T22:15:08.679887417Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:46:43.123867Z"}]}}