# CVE-2026-124278: Path bindings ignored for gRPC Content-Types on transcoded routes in elixir-grpc grpc_server

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

Authorization Bypass Through User-Controlled Key vulnerability in elixir-grpc grpc_server and grpc allows an attacker to make a handler act on a resource other than the one named in the URL of an HTTP-transcoded route, via a request with a gRPC Content-Type.

Only the transcoding clause of GRPC.Server.do_handle_request/4 (grpc_server/lib/grpc/server.ex, and lib/grpc/server.ex before the package split) applies the route's path bindings to the request message. The Cowboy handler picks that clause from the request Content-Type, not from the route. A request to a transcoded URL with application/grpc or application/grpc-web is decoded from the body alone, so every path-bound field takes its value from the body. A gateway, proxy rule or WAF that authorizes on the URL path sees one resource while the handler receives another.

This issue affects grpc_server: from 1.0.0 before 1.1.0; grpc: from 0.8.0 before 1.0.0.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/elixir-grpc/grpc/commit/953ab980d8a127e895d3ab9505fc4b9337bb32f7

## Affected products and versions

- elixir-grpc / grpc_server (grpc_server): ≥ 1.0.0; < 1.1.0 (affected, semver). Source: CNA: EEF
- elixir-grpc / grpc_server (elixir-grpc/grpc): ≥ 0332faae5f5e132314794dbfdae5edecbccea292; < 953ab980d8a127e895d3ab9505fc4b9337bb32f7 (affected, git). Source: CNA: EEF
- elixir-grpc / grpc (grpc): ≥ 0.8.0; < 1.0.0 (affected, semver). Source: CNA: EEF
- elixir-grpc / grpc (elixir-grpc/grpc): ≥ 8aaf3d3a8c4c7b08ac65e9c6f254e0d24da1d048; < 0332faae5f5e132314794dbfdae5edecbccea292 (affected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 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; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-436, CWE-639

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xc5v-89vq-hv5m (CNA: EEF; vendor-advisory, related)

- https://cna.erlef.org/cves/CVE-2026-124278.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-124278 (CNA: EEF; related)

- https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292 (CNA: EEF; related)

- https://github.com/elixir-grpc/grpc/commit/953ab980d8a127e895d3ab9505fc4b9337bb32f7 (CNA: EEF; patch)

- https://github.com/elixir-grpc/grpc/commit/8aaf3d3a8c4c7b08ac65e9c6f254e0d24da1d048 (CNA: EEF; related)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-124278; retrieved 2026-11-13; source updated 2026-11-13

Revision: 958d42bb8d1afdc00dad5e39e69efb57ab58f83aa4542ab1e54dff46bea7ef25

Canonical: https://y2.dev/cve/CVE-2026-124278

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.