{"id":"CVE-2026-47066","state":"PUBLISHED","title":"Infinite loop in Alt-Svc header parser in hackney","description":"Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in benoitc hackney allows Excessive Allocation. The Alt-Svc response header parser in src/hackney_altsvc.erl does not guarantee forward progress. When parse_token/2 receives a non-token, non-whitespace, non-comma byte (e.g. !, @, =, ;), it returns the input unchanged. skip_comma/1 also returns the buffer unchanged when the first byte is not a comma. parse_entries/2 then recurses with identical data, creating a tight infinite tail-recursive loop that pins a scheduler at 100% CPU. The calling process never returns.\n\nThe entry point parse_and_cache/3 is called synchronously in the connection process on every HTTP response. A single-byte Alt-Svc: ! response header is sufficient to trigger the hang; the header is fully controlled by any HTTP origin the client connects to.\n\nThis issue affects hackney: from 2.0.0-beta.1 before 4.0.1.","publishedAt":"2026-05-25T14:00:39.707Z","updatedAt":"2026-05-27T15:40:41.946Z","severity":{"score":8.7,"label":"High","version":"4.0","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","source":"EEF"},"assigner":"EEF","products":["benoitc hackney"],"affected":[{"vendor":"benoitc","product":"hackney","packageName":"hackney","packageURL":"pkg:hex/hackney","defaultStatus":"unaffected","versions":[{"version":"2.0.0-beta.1","status":"affected","lessThan":"4.0.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*"],"modules":["hackney_altsvc"],"programFiles":["src/hackney_altsvc.erl"],"programRoutines":[{"name":"hackney_altsvc:parse_entries/2"},{"name":"hackney_altsvc:parse_entry/1"},{"name":"hackney_altsvc:parse_protocol/1"},{"name":"hackney_altsvc:parse_token/2"},{"name":"hackney_altsvc:skip_comma/1"}],"repo":"https://github.com/benoitc/hackney"},{"vendor":"benoitc","product":"hackney","packageName":"benoitc/hackney","packageURL":"pkg:github/benoitc/hackney","defaultStatus":"unaffected","versions":[{"version":"408e5fe20302226ea8c74dde2bcbd452d712b5b2","status":"affected","lessThan":"e548aba1f97ffa3f4750da7b772998fb78c01894","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*"],"modules":["hackney_altsvc"],"programFiles":["src/hackney_altsvc.erl"],"programRoutines":[{"name":"hackney_altsvc:parse_entries/2"},{"name":"hackney_altsvc:parse_entry/1"},{"name":"hackney_altsvc:parse_protocol/1"},{"name":"hackney_altsvc:parse_token/2"},{"name":"hackney_altsvc:skip_comma/1"}],"repo":"https://github.com/benoitc/hackney"}],"references":["https://github.com/benoitc/hackney/security/advisories/GHSA-6cp8-v795-jr2j","https://cna.erlef.org/cves/CVE-2026-47066.html","https://osv.dev/vulnerability/EEF-CVE-2026-47066","https://github.com/benoitc/hackney/commit/e548aba1f97ffa3f4750da7b772998fb78c01894"],"weaknesses":["CWE-835"],"ingestedAt":"2026-10-29T20:12:07.131Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/47xxx/CVE-2026-47066.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-47066","state":"PUBLISHED","datePublished":"2026-05-25T14:00:39.707Z","dateUpdated":"2026-05-27T15:40:41.946Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-05-18T17:28:08.321Z"},"containers":{"cna":{"title":"Infinite loop in Alt-Svc header parser in hackney","descriptions":[{"lang":"en","value":"Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in benoitc hackney allows Excessive Allocation. The Alt-Svc response header parser in src/hackney_altsvc.erl does not guarantee forward progress. When parse_token/2 receives a non-token, non-whitespace, non-comma byte (e.g. !, @, =, ;), it returns the input unchanged. skip_comma/1 also returns the buffer unchanged when the first byte is not a comma. parse_entries/2 then recurses with identical data, creating a tight infinite tail-recursive loop that pins a scheduler at 100% CPU. The calling process never returns.\n\nThe entry point parse_and_cache/3 is called synchronously in the connection process on every HTTP response. A single-byte Alt-Svc: ! response header is sufficient to trigger the hang; the header is fully controlled by any HTTP origin the client connects to.\n\nThis issue affects hackney: from 2.0.0-beta.1 before 4.0.1."}],"affected":[{"vendor":"benoitc","product":"hackney","packageName":"hackney","packageURL":"pkg:hex/hackney","defaultStatus":"unaffected","versions":[{"version":"2.0.0-beta.1","status":"affected","lessThan":"4.0.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*"],"modules":["hackney_altsvc"],"programFiles":["src/hackney_altsvc.erl"],"programRoutines":[{"name":"hackney_altsvc:parse_entries/2"},{"name":"hackney_altsvc:parse_entry/1"},{"name":"hackney_altsvc:parse_protocol/1"},{"name":"hackney_altsvc:parse_token/2"},{"name":"hackney_altsvc:skip_comma/1"}],"repo":"https://github.com/benoitc/hackney"},{"vendor":"benoitc","product":"hackney","packageName":"benoitc/hackney","packageURL":"pkg:github/benoitc/hackney","defaultStatus":"unaffected","versions":[{"version":"408e5fe20302226ea8c74dde2bcbd452d712b5b2","status":"affected","lessThan":"e548aba1f97ffa3f4750da7b772998fb78c01894","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*"],"modules":["hackney_altsvc"],"programFiles":["src/hackney_altsvc.erl"],"programRoutines":[{"name":"hackney_altsvc:parse_entries/2"},{"name":"hackney_altsvc:parse_entry/1"},{"name":"hackney_altsvc:parse_protocol/1"},{"name":"hackney_altsvc:parse_token/2"},{"name":"hackney_altsvc:skip_comma/1"}],"repo":"https://github.com/benoitc/hackney"}],"references":[{"url":"https://github.com/benoitc/hackney/security/advisories/GHSA-6cp8-v795-jr2j","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-47066.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-47066","tags":["related"]},{"url":"https://github.com/benoitc/hackney/commit/e548aba1f97ffa3f4750da7b772998fb78c01894","tags":["patch"]}],"metrics":[{"cvssV4_0":{"attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":8.7,"baseSeverity":"HIGH","privilegesRequired":"NONE","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-835","description":"CWE-835 Loop with Unreachable Exit Condition ('Infinite Loop')","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-05-27T15:40:41.946Z"},"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*","versionEndExcluding":"4.0.1","versionStartIncluding":"2.0.0-beta.1","vulnerable":true}],"negate":false,"operator":"AND"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"Peter Ullrich"},{"lang":"en","type":"remediation developer","value":"Benoit Chesneau"},{"lang":"en","type":"analyst","value":"Jonatan Männchen / EEF"}],"impacts":[{"capecId":"CAPEC-130","descriptions":[{"lang":"en","value":"CAPEC-130 Excessive Allocation"}]}],"source":{"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/benoitc/hackney/security/advisories/GHSA-6cp8-v795-jr2j","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-05-26T15:50:47.725364Z","id":"CVE-2026-47066","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-05-26T15:50:51.330Z"}}]}}}