Uncontrolled recursion in elixir-protobuf/protobuf JSON decoding of self-referential messages

Summary

Uncontrolled Recursion vulnerability in Protobuf.JSON.Decode in elixir-protobuf protobuf allows an unauthenticated remote attacker to crash the decoding process via a deeply nested JSON document. Any application that decodes attacker-supplied JSON with Protobuf.JSON.decode/3, Protobuf.JSON.decode!/3, or Protobuf.JSON.from_decoded/3 into a schema that contains a self-referential or cyclic message type is affected. In lib/protobuf/json/decode.ex, the embedded-message clause of decode_singular/3 recurses into internal_from_json_data/3 once per nesting level without incrementing or checking the decoder's depth counter. The depth guard increase_depth_and_maybe_throw/1 covers only the Google.Protobuf.ListValue and Google.Protobuf.Struct clauses, so the recursion_limit option has no effect on user-defined message types. Each nesting level allocates a stack frame and heap objects, and a sufficiently deep document exhausts the memory of the decoding process. Confidentiality and integrity are not affected. This issue affects protobuf: from 0.8.0 before 0.17.1.

Timeline

1. Oct 9, 2026, 8:17 AM UTCCVE published
2. Oct 15, 2026, 3:56 PM UTCCISA SSVC assessment

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

3. Oct 15, 2026, 3:57 PM UTCRecord last updated

Affected versions

• protobuf

  From 0.8.0 · fixed in 0.17.1

• elixir-protobuf/protobuf

  From b0a1d4eaffaf50012fa71a8e931a47cf252d0370 · fixed in e9432ad1c4099511905353cebcececa3a1f7c3ff

• protobufHex

  From 0.8.0 · fixed in 0.17.1

References 5