HTTP/2 Rapid reset attack The HTTP/2 protocol allows clients to indicate to the server that a previous stream should be canceled by sending a RSTSTREAM frame. The protocol does not require the client and server to coordinate the cancellation in any way, the client may do it unilaterally. The client may also assume that the cancellation will take effect immediately when the server receives the RSTSTREAM frame, before any other data from that TCP connection is processed.

Abuse of this feature is called a Rapid Reset attack because it relies on the ability for an endpoint to send a RSTSTREAM frame immediately after sending a request frame, which makes the other endpoint start working and then rapidly resets the request. The request is canceled, but leaves the HTTP/2 connection open.

The HTTP/2 Rapid Reset attack built on this capability is simple: The client opens a large number of streams at once as in the standard HTTP/2 attack, but rather than waiting for a response to each request stream from the server or proxy, the client cancels each request immediately.

The ability to reset streams immediately allows each connection to have an indefinite number of requests in flight. By explicitly canceling the requests, the attacker never exceeds the limit on the number of concurrent open streams. The number of in-flight requests is no longer dependent on the round-trip time (RTT), but only on the available network bandwidth.

In a typical HTTP/2 server implementation, the server will still have to do significant amounts of work for canceled requests, such as allocating new stream data structures, parsing the query and doing header decompression, and mapping the URL to a resource. For reverse proxy implementations, the request may be proxied to the backend server before the RSTSTREAM frame is processed. The client on the other hand paid almost no costs for sending the requests. This creates an exploitable cost asymmetry between the server and the client.

Multiple software artifacts implementing HTTP/2 are affected. This advisory was originally ingested from the swift-nio-http2 repo advisory and their original conent follows.

swift-nio-http2 specific advisory swift-nio-http2 is vulnerable to a denial-of-service vulnerability in which a malicious client can create and then reset a large number of HTTP/2 streams in a short period of time. This causes swift-nio-http2 to commit to a large amount of expensive work which it then throws away, including creating entirely new Channels to serve the traffic. This can easily overwhelm an EventLoop and prevent it from making forward progress.

swift-nio-http2 1.28 contains a remediation for this issue that applies reset counter using a sliding window. This constrains the number of stream resets that may occur in a given window of time. Clients violating this limit will have their connections torn down. This allows clients to continue to cancel streams for legitimate reasons, while constraining malicious actors.

Istio is an open platform to connect, manage, and secure microservices. Prior to 1.29.1, 1.28.5, and 1.27.8, a user of Istio is impacted if the JWKS resolver becomes unavailable or the fetch fails, exposing hardcoded defaults regardless of use of the RequestAuthentication resource. This vulnerability is fixed in 1.29.1, 1.28.5, and 1.27.8.

Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. According to RFC 4343, Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname "httpbin.foo" for some source IPs, but the attacker can bypass this by sending the request with hostname "Httpbin.Foo". Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the Security Best Practices guide.

Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. Istio 1.11.0, 1.10.3 and below, and 1.9.7 and below contain a remotely exploitable vulnerability where an HTTP request with #fragment in the path may bypass Istio’s URI path based authorization policies. Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize the path.

An issue was discovered in Istio 1.3 through 1.3.6. Under certain circumstances, it is possible to bypass a specifically configured Mixer policy. Istio-proxy accepts the x-istio-attributes header at ingress that can be used to affect policy decisions when Mixer policy selectively applies to a source equal to ingress. To exploit this vulnerability, someone has to encode a source.uid in this header. This feature is disabled by default in Istio 1.3 and 1.4.

A flaw was found in Istio in all versions released after 1.3 (included). The flaw is in Istio's Authentication Policy exact path matching logic and can allow unauthorized access to a HTTP path, even if the path is configured to be only accessed with a valid JWT token.

End of life: 11/30/2026, Latest version: 1.30.3

Istio is an open platform to connect, manage, and secure microservices. Prior to versions 1.28.6 and 1.29.2, when a RequestAuthentication resource is created with a jwksUri pointing to an internal service, istiod makes an unauthenticated HTTP GET request to that URL without filtering out localhost or link local ips. This can result in sensitive data being distributed to Envoy proxies via xDS configuration. This issue has been patched in versions 1.28.6 and 1.29.2.

Impact The serviceAccounts and notServiceAccounts fields in AuthorizationPolicy incorrectly interpret dots (.) as a regular expression matcher. Because . is a valid character in a service account name, an AuthorizationPolicy ALLOW rule targeting SA e.g. cert-manager.io also matches cert-manager-io, cert-managerXio, etc. A DENY rule targeting the same name fails to block those variants.

Patches Fixes are available in 1.29.2, 1.28.6, and 1.27.9

Workarounds None

Istio is an open platform to connect, manage, and secure microservices. Prior to 1.29.1, 1.28.5, and 1.27.8, a vulnerability in Envoy RBAC header matching could allow authorization policy bypass when policies rely on HTTP headers that may contain multiple values. An attacker could craft requests with multiple header values in a way that causes Envoy to evaluate the header differently than intended, potentially bypassing authorization checks. This may allow unauthorized requests to reach protected services when policies depend on such header-based matching conditions. This vulnerability is fixed in 1.29.1, 1.28.5, and 1.27.8.

Istio is an open platform to connect, manage, and secure microservices. Prior to 1.29.1, 1.28.5, and 1.27.8, a user of Istio is impacted if the JWKS resolver becomes unavailable or the fetch fails, exposing hardcoded defaults regardless of use of the RequestAuthentication resource. This vulnerability is fixed in 1.29.1, 1.28.5, and 1.27.8.

End of life: 8/31/2026, Latest version: 1.29.6

End of life: 7/1/2026, Latest version: 1.28.10

End of life: 4/7/2026, Latest version: 1.27.9

A stack exhaustion flaw was found in the Istio control plane. This flaw allows a remote unauthenticated attacker to send a specially crafted or oversized message to crash the control plane process, resulting in a denial of service condition.

End of life: 12/22/2025, Latest version: 1.26.8

Istio is an open platform to connect, manage, and secure microservices. In Istio 1.12.0 and 1.12.1 The authorization policy with hosts and notHosts might be accidentally bypassed for ALLOW action or rejected unexpectedly for DENY action during the upgrade from 1.11 to 1.12.0/1.12.1. Istio 1.12 supports the hosts and notHosts fields in authorization policy with a new Envoy API shipped with the 1.12 data plane. A bug in the 1.12.0 and 1.12.1 incorrectly uses the new Envoy API with the 1.11 data plane. This will cause the hosts and notHosts fields to be always matched regardless of the actual value of the host header when mixing 1.12.0/1.12.1 control plane and 1.11 data plane. Users are advised to upgrade or to not mix the 1.12.0/1.12.1 control plane with 1.11 data plane if using hosts or notHosts field in authorization policy.

Istio is an open platform to connect, manage, and secure microservices. In versions 1.12.0 and 1.12.1 Istio is vulnerable to a privilege escalation attack. Users who have CREATE permission for gateways.gateway.networking.k8s.io objects can escalate this privilege to create other resources that they may not have access to, such as Pod. This vulnerability impacts only an Alpha level feature, the Kubernetes Gateway API. This is not the same as the Istio Gateway type (gateways.networking.istio.io), which is not vulnerable. Users are advised to upgrade to resolve this issue. Users unable to upgrade should implement any of the following which will prevent this vulnerability: Remove the gateways.gateway.networking.k8s.io CustomResourceDefinition, set PILOTENABLEGATEWAYAPIDEPLOYMENTCONTROLLER=true environment variable in Istiod, or remove CREATE permissions for gateways.gateway.networking.k8s.io objects from untrusted users.

A flaw was found in istio. This flaw allows an attacker to send a specially crafted message to isitiod, causing the control plane to crash.

A flaw was found in Istio. Memory access violation of ill-formed headers sent to Envoy in certain configurations can lead to unexpected memory access, resulting in undefined behavior or crashing.

An uncontrolled resource consumption flaw was found in the Istio control plane, istiod. This issue could allow an unauthenticated remote attacker to send a specially crafted or oversized message that could cause a denial of service.

Istio is an open platform to connect, manage, and secure microservices. In versions on the 1.15.x branch prior to 1.15.3, a user can impersonate any workload identity within the service mesh if they have localhost access to the Istiod control plane. Version 1.15.3 contains a patch for this issue. There are no known workarounds.

End of life: 9/30/2025, Latest version: 1.25.5

End of life: 4/16/2025, Latest version: 1.23.6

End of life: 4/16/2025, Latest version: 1.23.6

End of life: 6/24/2025, Latest version: 1.24.6

End of life: 6/24/2025, Latest version: 1.24.6

End of life: 1/22/2025, Latest version: 1.22.8

End of life: 1/22/2025, Latest version: 1.22.8

End of life: 9/27/2024, Latest version: 1.21.6