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 decoders 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.
Weakness
The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.
Potential Mitigations
Related Attack Patterns
References
- https://cna.erlef.org/cves/CVE-2026-104635.html
- https://github.com/elixir-protobuf/protobuf/commit/b0a1d4eaffaf50012fa71a8e931a47cf252d0370
- https://github.com/elixir-protobuf/protobuf/commit/e9432ad1c4099511905353cebcececa3a1f7c3ff
- https://github.com/elixir-protobuf/protobuf/security/advisories/GHSA-m497-c2h9-rvw6
- https://osv.dev/vulnerability/EEF-CVE-2026-104635
- https://osv.dev/vulnerability/EEF-CVE-2026-104635