Weakness Type (CWE)

CWE-835 — CWE-835 Loop with Unreachable Exit Condition ('Infinite Loop')

CAPEC

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

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.

The 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.

This issue affects hackney: from 2.0.0-beta.1 before 4.0.1.

Affected

pkg:hex/hackney

Module Source File Routine
hackney_altsvc src/hackney_altsvc.erl hackney_altsvc:parse_entries/2
hackney_altsvc:parse_entry/1
hackney_altsvc:parse_protocol/1
hackney_altsvc:parse_token/2
hackney_altsvc:skip_comma/1
Status Type Version Changes / Fixed in
affected semver ⓘ 2.0.0-beta.1 < 4.0.1

pkg:github/benoitc/hackney

Module Source File Routine
hackney_altsvc src/hackney_altsvc.erl hackney_altsvc:parse_entries/2
hackney_altsvc:parse_entry/1
hackney_altsvc:parse_protocol/1
hackney_altsvc:parse_token/2
hackney_altsvc:skip_comma/1
Status Type Version Changes / Fixed in
affected git ⓘ 408e5fe203 < e548aba1f9

References

Credits

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

CVE record as JSON:  GET /cves/CVE-2026-47066.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-47066.json