CVE-2026-104635 Uncontrolled recursion in elixir-protobuf/protobuf JSON decoding of self-referential messages
An unauthenticated remote attacker can crash the decoding process by sending a deeply nested JSON document to applications using the Elixir protobuf library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-104635?
CVE-2026-104635 is a high-severity denial of service vulnerability in elixir-protobuf protobuf, published on 9 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-674
Which versions are affected by CVE-2026-104635?
1 open source package ship an affected version, including protobuf.
| Package | Affected | Fixed in |
|---|---|---|
protobuf Hex | From 0.8.0 | 0.17.1 |
How do I fix CVE-2026-104635?
Upgrade protobuf to 0.17.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-104635 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-104635 exists.
Sources
Also known as EEF-CVE-2026-104635, GHSA-m497-c2h9-rvw6.