Unbounded recursion between Inspect.List charlist rendering and List.to_string/1 error path in Elixir

Summary

Uncontrolled Recursion vulnerability in the Elixir standard library allows an attacker who controls a list passed to inspect/1, List.to_string/1, or List.to_charlist/1 to exhaust a BEAM node's memory. Inspect.List's charlist branch in lib/elixir/lib/inspect.ex classifies a list as a charlist using List.ascii_printable?/2, which examines only the first :printable_limit (4096 by default) elements, and then calls IO.chardata_to_string/1 on the whole term. A list whose printable prefix exceeds that limit but which contains a later element that is not a code point (an atom, an out-of-range integer, or an improper tail) is therefore mis-classified, and the conversion raises ArgumentError. That conversion runs inside List.to_string/1, whose rescue clause builds its message by interpolating inspect(list), which re-enters the same branch and raises again. The nested inspection is an argument to raise, so the recursion is not in tail position and every level is retained: the process stack grows monotonically while each cycle re-walks the list, until the process is killed by max_heap_size or, by default, the node runs out of memory. List.to_charlist/1 has the same rescue shape. Below the printable limit the inner inspect/1 sees the invalid element within its counter and renders the list in ordinary bracket form, so a single ArgumentError is raised and no recursion occurs. This issue affects elixir: from 1.15.0-rc.0 before 1.18.5, from 1.19.0-rc.0 before 1.19.6, and from 1.20.0-rc.0 before 1.20.4.

Timeline

1. Aug 28, 2026, 11:28 AM UTCCVE published
2. Aug 28, 2026, 6:28 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Aug 28, 2026, 6:29 PM UTCRecord last updated

Affected versions

• elixir

  From 1.15.0-rc.0 · fixed in 1.18.5; From 1.19.0-rc.0 · fixed in 1.19.6; From 1.20.0-rc.0 · fixed in 1.20.4

• elixir-lang/elixir

  Version range not reported

References 7