{"id":"CVE-2026-47077","title":"Hackney: Per-chunk timeout with unbounded body accumulation enables slow-drip OOM","summary":"Hackney: Per-chunk timeout with unbounded body accumulation enables slow-drip OOM","severity":"high","cwe":["CWE-295","CWE-400"],"vendor":"hackney","product":"hackney","ecosystem":"erlang","affected":["hackney >= 2.0.0, < 4.0.1"],"patched":["hackney 4.0.1"],"published":"2026-06-26","updated":"2026-06-30","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-jq4m-q6p2-8gwc","references":[{"url":"https://github.com/benoitc/hackney/security/advisories/GHSA-jq4m-q6p2-8gwc"},{"url":"https://github.com/ex-aws/ex_aws_sns/security/advisories/GHSA-8jgf-23q5-x7xx"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-47077"},{"url":"https://github.com/benoitc/hackney/commit/3d25f9fea26c90609de9d64366fedfe5065413bc"},{"url":"https://cna.erlef.org/cves/CVE-2026-47077.html"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-47077"},{"url":"https://github.com/advisories/GHSA-jq4m-q6p2-8gwc"}],"tags":["ghsa","erlang"],"epss":0.00703,"epssPercentile":0.51467,"ingestedAt":"2026-06-30T17:40:12.504Z","slug":"CVE-2026-47077","body":"## Overview\n\n### Summary\n\n`hackney_h3:await_response_loop/6` in `src/hackney_h3.erl` accumulates the HTTP/3 response body in memory without any size cap. The `after Timeout` clause is a per-message inactivity timer, not a wall-clock deadline: every received `stream_data` chunk, housekeeping `select` message, or `settings` frame resets it. A malicious HTTP/3 server that drips one small chunk every `Timeout - 1` ms with `Fin = false` and never terminates the stream keeps the loop alive indefinitely while the accumulation buffer grows without bound, eventually exhausting the BEAM process heap.\n\n### Details\n\nIn `src/hackney_h3.erl`, `await_response_loop/6` (line 430) builds the body with:\n\n```erlang\nNewBody = <<AccBody/binary, Data/binary>>\n```\n\nThere is no `max_body` check and no monotonic deadline. The `after Timeout` clause at line 463 is restarted on each loop iteration. A server that ensures at least one message arrives within `Timeout` ms indefinitely (one small chunk per interval is sufficient) prevents the timeout from firing while `AccBody` grows linearly. The same module's `wait_connected/3` (lines 388-389) shows the correct pattern: track an absolute start time and pass a shrinking `Remaining` budget into each `receive`. This loop does not.\n\n### Configurations\n\nOnly the HTTP/3 transport is affected. Applications using the default TCP/TLS hackney transport are not vulnerable. The vulnerability requires using `hackney_h3` directly or passing `{transport, h3}` to `hackney:request/5`.\n\n### PoC\n\n1. Stand up an HTTP/3 server that responds with `200 OK` headers (`Fin = false`), then emits a small `stream_data` chunk every `Timeout - margin` ms with `Fin = false` indefinitely.\n2. Issue `hackney:request(get, Url, [], <<>>, [{transport, h3}])` against it.\n3. Watch the client process heap grow monotonically. The configured timeout never fires; the process is eventually killed by `max_heap_size` or the OS OOM killer.\n\n### Impact\n\nRemote denial of service via unbounded memory consumption. Affects hackney 2.0.0 through 4.0.0 when using the HTTP/3 transport against an attacker-controlled or attacker-influenced server. Each affected request consumes unbounded memory until the BEAM is killed. CVSS v4.0: **8.2 (HIGH)**.\n\n## Resources\n\n* Introduction commit: https://github.com/benoitc/hackney/commit/0334af206d5099fdf510ed9eda18e34396f065ad\n* Patch commit: https://github.com/benoitc/hackney/commit/3d25f9fea26c90609de9d64366fedfe5065413bc\n\n## Affected packages\n\n- `hackney >= 2.0.0, < 4.0.1`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `hackney 4.0.1`","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}