Atom table exhaustion via unrecognized URL schemes in hackney

Weakness Type (CWE)

CWE-770 — CWE-770 Allocation of Resources Without Limits or Throttling

CAPEC

CAPEC-125 — CAPEC-125 Flooding

CVSS 4.0 Score

8.7

HIGH

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

Vulnerability 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.

This issue affects hackney: from 2.0.0 before 4.0.1.

Affected

`pkg:hex/hackney`

Module	Source File	Routine
`hackney_url`	`src/hackney_url.erl`	`hackney_url:parse_url/1`

Status	Type	Version	Changes / Fixed in
affected	semver ^ⓘ	`2.0.0`	< `4.0.1`

`pkg:github/benoitc/hackney`

Module	Source File	Routine
`hackney_url`	`src/hackney_url.erl`	`hackney_url:parse_url/1`

Status	Type	Version	Changes / Fixed in
affected	git ^ⓘ	`d9713695c0`	< `31f6f0e27e`

References

https://github.com/benoitc/hackney/security/advisories/GHSA-9653-rcfr-5c62 vendor-advisory related
https://osv.dev/vulnerability/EEF-CVE-2026-47067 related
https://github.com/benoitc/hackney/commit/31f6f0e27e096ad88743dfded4f030a3ee74972e patch

Credits

Finder: Peter Ullrich
Remediation developer: Benoit Chesneau
Analyst: Jonatan Männchen

CVE record as JSON: GET /cves/CVE-2026-47067.json
OSV record as JSON: GET /osv/EEF-CVE-2026-47067.json