Weakness Type (CWE)

CWE-639 — CWE-639 Authorization Bypass Through User-Controlled Key

CAPEC

CVSS 4.0 Score

7.6

HIGH

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

Vulnerability 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.

Affected

pkg:hex/grpc

Module Source File Routine
GRPC.Server.Transcode lib/grpc/server/transcode.ex GRPC.Server.Transcode.map_request/5
Status Type Version Changes / Fixed in
affected semver ⓘ 0.8.0 < 1.0.0

pkg:github/elixir-grpc/grpc

Module Source File Routine
GRPC.Server.Transcode lib/grpc/server/transcode.ex GRPC.Server.Transcode.map_request/5
Status Type Version Changes / Fixed in
affected git ⓘ 8aaf3d3a8c < 33b6a095db

Configurations

HTTP-to-gRPC transcoding must be enabled.

References

Credits

  • Finder: Peter Ullrich
  • Remediation developer: Paulo Valente
  • Analyst: Jonatan Männchen

CVE record as JSON:  GET /cves/CVE-2026-48599.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-48599.json