envoy

Breaking changes

What to check before upgrading, taken from the notes of the last 30 releases.

• v1.40.0Oct 13, 2026

  Breaking changes

  • build: Envoy has switched from WORKSPACE to bzlmod. The WORKSPACE file is removed; Envoy, the API and the docs are published as Bazel modules (envoy, envoy_api, envoy-docs). Downstreams must migrate to MODULE.bazel and must add Envoy's custom registry (https://raw.githubusercontent.com/envoyproxy/bazel-registry) alongside the BCR — many of Envoy's dependencies and patched modules are only published there.
  • build: the hermetic LLVM/Clang toolchain is bumped from 18 to 22. --config=clang and clang-local are removed — Clang/libc++ is now the default and needs no flag; GCC remains via --config=gcc. The --@envoy//bazel:libc++/libstdc++ flags and force_libcpp define are gone. Downstreams needing a host LLVM toolchain should follow bazel/tests/codeql.
  • build: the Wasm runtime is now selected with --@proxy-wasm-cpp-host//bazel:engine=; the old --define wasm=/--define engine= flags fail the build.
  • tls: AWS-LC is removed as a selectable SSL library (including --config=aws-lc-fips). ppc64le builds should use --config=openssl.
  • mcp_router: downstream request headers are no longer forwarded to backends by default — notably authorization. Use the new per-backend header_forwarding (forward_all: true restores the old behavior).
  • dynamic modules (Rust SDK): HttpFilter hooks now take &self rather than &mut self; per-stream mutable state must move behind interior mutability. This closes a use-after-free on synchronous filter-chain teardown.

  Deprecations

  • envoy.extensions.config.validators factories keyed by type URL; dynamic-module log and timing-info callbacks; legacy HTTP filter factory base classes; reverse-tunnel auto_close_connections; Wasm plugin-level capability restriction.

  Docker images:

  https://hub.docker.com/r/envoyproxy/envoy/tags?page=1&name=v1.40.0

  Docs:

  https://www.envoyproxy.io/docs/envoy/v1.40.0/

  Release notes:

  https://www.envoyproxy.io/docs/envoy/v1.40.0/version_history/v1.40/v1.40.0

  Full changelog:

  https://github.com/envoyproxy/envoy/compare/v1.39.0...v1.40.0

  Signed-off-by: Jonh Wendell

  Signed-off-by: Ryan Northey

• v1.39.0Jul 14, 2026

  Breaking changes

  • build: Envoy now uses Bazel 8. Because Envoy still uses WORKSPACE mode, --enable_workspace and --noenable_bzlmod are required and have been added to .bazelrc; external-repository runfiles now appear directly under the runfiles root.
  • build: the Intel DLB connection balancer (envoy.network.connection_balance.dlb) is disabled for all builds due to a broken source archive.
  • TLS: enforce_rsa_key_usage is deprecated and ignored; Envoy now always enforces the certificate keyUsage extension.
  • TLS inspector: client TLS versions are validated and must be between TLS 1.0 and TLS 1.3 (revertible via envoy.reloadable_features.tls_inspector_enforce_client_tls_version).
  • OpenTelemetry tracing: the tracer now honors Envoy's request-entry sampling decision, including overall_sampling, even when propagated trace context or the configured sampler requests sampling. This may reduce exported spans.

  Security

  • HTTP/2 now counts uncompressed cookies toward header-size and header-count limits (CVE-2026-47774), strengthens PRIORITY/WINDOW_UPDATE flood protection, and adds configurable nghttp2 RST_STREAM rate limits.
  • HTTP/3 fixes cover QPACK blocked-decoding denial of service (GHSA-p7c7-7c47-pwch) and inconsistent headers-only content-length handling (CVE-2026-48743).
  • Security fixes were added for ext_authz (CVE-2026-47205), ext_proc (CVE-2026-47207), gRPC stats (CVE-2026-47204), internal redirects (CVE-2026-47221), and OAuth2 lifecycle handling (CVE-2026-48090).
  • OAuth2 adds AES-256-GCM cookie encryption to address CVE-2026-47775. Migration is opt-in: enable oauth2_use_gcm_encryption, monitor oauth_legacy_cbc_decrypt, then disable oauth2_legacy_cbc_decrypt_compat.
  • Additional fixes cover DNS query validation (CVE-2026-48497), JSON nesting limits (CVE-2026-48042), PROXY protocol TLV smuggling (CVE-2026-47692), formatter crashes (CVE-2026-47220), TCP StatsD overflow (CVE-2026-48706), TLS SAN NUL handling (CVE-2026-47778), and Zstd decompression memory exhaustion (CVE-2026-48044).
  • New upstream RBAC and dynamic-forward-proxy resolved-address filtering provide CIDR-based protection against SSRF after DNS resolution and host selection.

  Dynamic modules

  • New extension points: access-log/header formatters, downstream and upstream transport sockets, active health checkers, and stats sinks.
  • Cluster load balancers can read host stats, read and write dynamic metadata and filter state, and publish main-thread state to worker-local slots.
  • Modules can emit metrics from configuration and background contexts; loading and initialization failures now expose server-wide counters tagged by extension instance.
  • Added validation-mode detection, network/listener attribute access, batched header and metadata APIs, effective log-level access, and zero-copy borrowed buffers in the Rust SDK.
  • Fixed listener HTTP-callout crashes, watermark initialization, streaming-response re-entry, independent decode/encode continuation, CatchUnwind re-entry, Struct configuration handling, and HTTP/TCP bridge buffer overflow with more than 64 slices.

  MCP (Model Context Protocol) and AI protocols

  • Added a Wuffs-backed streaming JSON parser for MCP, A2A, OpenAI, Anthropic, and related protocols, with bounded field capture, incremental parsing, no DOM allocation, and duplicate-key detection.
  • MCP filtering now exposes processing status, supports configurable duplicate-key rejection, and improves oversized-body behavior for pass-through and rejection modes.
  • MCP router adds elicitation and server-to-client request routing, plus lazy per-backend initialization.
  • MCP JSON REST Bridge adds per-route tool configuration and locally generated tools/list responses.