# 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.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Oct 2026
- **Updated:** 15 Oct 2026
- **Also known as:** EEF-CVE-2026-104635, GHSA-m497-c2h9-rvw6

## 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 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-104635?

1 open source package ship an affected version, including protobuf.


| Package | Ecosystem | 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.

## Is CVE-2026-104635 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-104635 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-104635 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-104635 exists.

Affected packages and fixed versions:
- protobuf (Hex): affected from 0.8.0; fixed in 0.17.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-104635/ (Markdown: https://insights.sbomify.com/CVE-2026-104635/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-104635
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-104635
- OSV: https://osv.dev/vulnerability/CVE-2026-104635

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-104635/
Summaries are generated and may contain mistakes; the official description above is the record.