chore(all): update module google.golang.org/grpc to v1.79.3 [SECURITY] (main) (#14201)

This PR contains the following updates:

| Package | Change |
[Age](https://docs.renovatebot.com/merge-confidence/) |
[Confidence](https://docs.renovatebot.com/merge-confidence/) |
|---|---|---|---|
| [google.golang.org/grpc](https://redirect.github.com/grpc/grpc-go) |
`v1.79.2` → `v1.79.3` |
![age](https://developer.mend.io/api/mc/badges/age/go/google.golang.org%2fgrpc/v1.79.3?slim=true)
|
![confidence](https://developer.mend.io/api/mc/badges/confidence/go/google.golang.org%2fgrpc/v1.79.2/v1.79.3?slim=true)
|

### GitHub Vulnerability Alerts

####
[CVE-2026-33186](https://redirect.github.com/grpc/grpc-go/security/advisories/GHSA-p77j-4mvh-x3m3)

### Impact
_What kind of vulnerability is it? Who is impacted?_

It is an **Authorization Bypass** resulting from **Improper Input
Validation** of the HTTP/2 `:path` pseudo-header.

The gRPC-Go server was too lenient in its routing logic, accepting
requests where the `:path` omitted the mandatory leading slash (e.g.,
`Service/Method` instead of `/Service/Method`). While the server
successfully routed these requests to the correct handler, authorization
interceptors (including the official `grpc/authz` package) evaluated the
raw, non-canonical path string. Consequently, "deny" rules defined using
canonical paths (starting with `/`) failed to match the incoming
request, allowing it to bypass the policy if a fallback "allow" rule was
present.

**Who is impacted?**
This affects gRPC-Go servers that meet both of the following criteria:
1. They use path-based authorization interceptors, such as the official
RBAC implementation in `google.golang.org/grpc/authz` or custom
interceptors relying on `info.FullMethod` or `grpc.Method(ctx)`.
2. Their security policy contains specific "deny" rules for canonical
paths but allows other requests by default (a fallback "allow" rule).

The vulnerability is exploitable by an attacker who can send raw HTTP/2
frames with malformed `:path` headers directly to the gRPC server.

### Patches
_Has the problem been patched? What versions should users upgrade to?_

Yes, the issue has been patched. The fix ensures that any request with a
`:path` that does not start with a leading slash is immediately rejected
with a `codes.Unimplemented` error, preventing it from reaching
authorization interceptors or handlers with a non-canonical path string.

Users should upgrade to the following versions (or newer):
* **v1.79.3**
* The latest **master** branch.

It is recommended that all users employing path-based authorization
(especially `grpc/authz`) upgrade as soon as the patch is available in a
tagged release.

### Workarounds
_Is there a way for users to fix or remediate the vulnerability without
upgrading?_

While upgrading is the most secure and recommended path, users can
mitigate the vulnerability using one of the following methods:

#### 1. Use a Validating Interceptor (Recommended Mitigation)
Add an "outermost" interceptor to your server that validates the path
before any other authorization logic runs:

```go
func pathValidationInterceptor(ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
    if info.FullMethod == "" || info.FullMethod[0] != '/' {
        return nil, status.Errorf(codes.Unimplemented, "malformed method name")
    }   
    return handler(ctx, req)
}

// Ensure this is the FIRST interceptor in your chain
s := grpc.NewServer(
    grpc.ChainUnaryInterceptor(pathValidationInterceptor, authzInterceptor),
)
```

#### 2. Infrastructure-Level Normalization
If your gRPC server is behind a reverse proxy or load balancer (such as
Envoy, NGINX, or an L7 Cloud Load Balancer), ensure it is configured to
enforce strict HTTP/2 compliance for pseudo-headers and reject or
normalize requests where the `:path` header does not start with a
leading slash.

#### 3. Policy Hardening
Switch to a "default deny" posture in your authorization policies
(explicitly listing all allowed paths and denying everything else) to
reduce the risk of bypasses via malformed inputs.

---

### Release Notes

<details>
<summary>grpc/grpc-go (google.golang.org/grpc)</summary>

###
[`v1.79.3`](https://redirect.github.com/grpc/grpc-go/releases/tag/v1.79.3):
Release 1.79.3

[Compare
Source](https://redirect.github.com/grpc/grpc-go/compare/v1.79.2...v1.79.3)

### Security

- server: fix an authorization bypass where malformed :path headers
(missing the leading slash) could bypass path-based restricted "deny"
rules in interceptors like `grpc/authz`. Any request with a
non-canonical path is now immediately rejected with an `Unimplemented`
error.
([#&#8203;8981](https://redirect.github.com/grpc/grpc-go/issues/8981))

</details>

---

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---------

Co-authored-by: Seth Hollyman <shollyman@google.com>