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CVE-2026-48599 — grpc

Fix: elixir-grpc/grpc@33b6a09

CVE-2026-48599 is a CWE-639 vulnerability in grpc. A fix is available for grpc — see the affected versions and patch details below.

Authorization bypass via path binding override in elixir-grpc/grpc HTTP transcoding

Also known asEEF-CVE-2026-48599GHSA-mwr4-5g34-j5cq
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-48599.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs25th percentile — riskier than 25% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected
💧grpc

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.

Description

Summary

In the HTTP-to-gRPC transcoding layer of the grpc Hex package, query-string and request-body parameters can silently overwrite path-bound fields when building the decoded protobuf request struct. An authenticated attacker who can reach a transcoded endpoint can substitute any path-bound identifier (e.g. user_id from /users/{user_id}/profile) with an arbitrary value, bypassing authorization, multi-tenancy, and ownership checks that rely on the path-derived field.

Details

All three clauses of GRPC.Server.Transcode.map_request/5 (grpc_server/lib/grpc/server/transcode.ex) use Map.merge/2 with path bindings as the first argument, giving them the lowest merge precedence. Path bindings are extracted by the router from the matched URL template and should be the authoritative resource identifiers, but query-string and body parameters overwrite them. The decoded protobuf struct handed to the handler carries the attacker's value instead of the router's.

PoC

  1. Deploy a transcoded gRPC service with a route like GET /users/{user_id}/profile where the handler authorizes access based on request.user_id.
  2. Send: GET /users/me/profile?user_id=victim
  3. The decoded request struct has user_id = "victim" — the authorization check passes for the victim's resource, not the caller's.
  4. Alternatively, for a POST with body: "*": send {"user_id": "victim"} in the JSON body.

Impact

Affects applications using grpc ≥ 0.8.0 with HTTP transcoding enabled that rely on path-bound fields for authorization or tenant isolation. Fixed in 1.0.0. An authenticated attacker can read or modify any other user's resources exposed via transcoded endpoints.

References

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
💧Hexgrpc≥ 0.8.0&&< 1.0.01.0.0mix deps.update grpc

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for grpc, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update grpc to 1.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48599 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Summary In the HTTP-to-gRPC transcoding layer of the `grpc` Hex package, query-string and request-body parameters can silently overwrite path-bound fields when building the decoded protobuf request struct. An authenticated attacker who can reach a transcoded endpoint can substitute any path-bound identifier (e.g. `user_id` from `/users/{user_id}/profile`) with an arbitrary value, bypassing authorization, multi-tenancy, and ownership checks that rely on the path-derived field. ### Details All three clauses of `GRPC.Server.Transcode.map_request/5` (`grpc_server/lib/grpc/server/transcode.e
O3 Security · Impact-Aware SCA

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CVE-2026-48599: grpc — Fixed in 1.0.0