BREAKING CHANGES:

• acl: Tokens that hold service:write but not mesh:write will now receive a permission-denied error when attempting to attach builtin/lua or builtin/wasm EnvoyExtensions (or upstream envoy_listener_json/envoy_cluster_json escape-hatch overrides) to a service-defaults config entry, or when registering a connect-proxy sidecar with bootstrap or xDS escape-hatch keys set in the top-level Proxy.Config map or per-upstream in Proxy.Upstreams[*].Config. Operators must grant mesh:write to any token that legitimately needs these capabilities. [GH-23864]
• fips: (Enterprise only) FIPS release artifacts are renamed. Version metadata changes from +ent.fips1402 to +ent.fips1403, and package and container artifacts change from the F2 suffix to F3 (for example, consul-F2_1.20.4-1_amd64.deb becomes consul-F3_1.20.4-1_amd64.deb). Pipelines that pin FIPS artifact names or version strings must be updated. SECURITY:
• Upgrade go version to 1.26.7 to address security vulnerabilities. [GH-23869]
• acl: Require mesh:write in addition to service:write when attaching code-executing EnvoyExtensions (builtin/lua, builtin/wasm) or upstream escape-hatch overrides (envoy_listener_json, envoy_cluster_json in UpstreamConfig defaults or overrides) to a service-defaults config entry. Previously a holder of service:write on a service could attach a Lua script or Wasm module, or an upstream escape-hatch override, that Envoy compiled and executed on every proxied request as the sidecar process user, with access to mTLS private keys, request bodies, and the host filesystem. [GH-23864]
• acl: Require mesh:write in addition to service:write when registering a connect-proxy sidecar with bootstrap or xDS escape-hatch keys, whether set in the top-level Proxy.Config map or per-upstream in Proxy.Upstreams[*].Config (envoy_bootstrap_json_tpl, envoy_extra_static_listeners_json, envoy_public_listener_json, envoy_listener_json, envoy_cluster_json, envoy_local_cluster_json, envoy_extra_static_clusters_json, envoy_extra_stats_sinks_json, envoy_tracing_json, envoy_stats_config_json, envoy_listener_tracing_json). Key matching is case-insensitive to match the mapstructure decoding used downstream. Previously a holder of service:write on the proxy and its destination could inject arbitrary Envoy filter chain configuration into the sidecar bootstrap or xDS resources, including via a per-upstream override or a mixed-case key. [GH-23864]
• agent: Fixed a pre-authorization memory exhaustion vulnerability where an mTLS-authenticated RPC client with no ACL token could terminate a Consul server by sending a MessagePack request header with a large declared length. The MessagePack decoder allocated a byte slice of the declared size before method lookup, ACL token validation, or the rate-limiting interceptor could run, allowing a single oversized header to OOM-kill the server process. Two mitigations are applied:

1. Each RPC request header is now validated against RPCMaxHeaderBytes (default 512 bytes) before it is decoded. Every length prefix in the header is checked against the limit, so an oversized value is rejected before the decoder allocates memory for it, and the connection is closed before any ACL evaluation. Request bodies remain unbounded by this limit.
2. A per-request read deadline (reusing RPCHandshakeTimeout) is applied inside handleConsulConn and handleInsecureConn so that a slow attacker trickling an oversized header cannot retain a goroutine and logical heap indefinitely.

• catalog: Fixed an incorrect authorization vulnerability where a local ACL token with service:write or node:write could delete peer-imported catalog objects by supplying a non-default PeerName in a Catalog.Deregister request. Authorization was checked only against the local service or node name, not the peer origin, allowing deletion of objects in a peer-scoped catalog namespace the caller does not control. Catalog.Deregister now rejects any request whose PeerName is not the default, mirroring the existing guard on Catalog.Register and Catalog.ListServices. Legitimate peer-state deletion continues through the internal PeeringBackend.CatalogDeregister path.
• security: Upgrade golang.org/x/mod to v0.41.0, golang.org/x/crypto to v0.57.0, and golang.org/x/net to v0.59.0 to address security vulnerabilities. [GH-23913]
• xds: escape regex metacharacters in service name, namespace, partition, and trust domain values when building Envoy RBAC SPIFFE match patterns, preventing an intention/authorization bypass via regex injection. IMPROVEMENTS:
• fips: (Enterprise only) Migrate FIPS builds from FIPS 140-2 (BoringCrypto/CNG cgo toolchain) to FIPS 140-3 using the Go Cryptographic Module (GOFIPS140=v1.0.0, CMVP Certificate #5247). The runtime FIPS line now reports FIPS 140-3 Enabled, crypto module v1.0.0. FIPS builds no longer require cgo or a vendored Go toolchain. FIPS 140-2 and FIPS 140-3 agents are permitted to join the same cluster; rolling upgrades from +ent.fips1402 to +ent.fips1403 are supported. BUG FIXES:
• api-gateway: Fix a cold-start crash where an api-gateway's Envoy proxy could segfault during worker startup when a route's failover upstream was rendered as an aggregate cluster before its endpoints were assembled. Consul now holds each xDS stream's first push until the gateway's discovery-chain endpoints are ready (per-stream, first-push only, skipped for streams Envoy resumes, and bounded by a 30s deadline), and renders a failover upstream as a plain EDS cluster instead of an aggregate whenever its member endpoints are not yet available -- restoring full failover automatically once they arrive. Steady-state updates are never withheld. [GH-23892]
• mesh: (Enterprise only) Fix named-port upstreams to a multiport service that has a configured service-router, service-splitter, or service-resolver. The service's declared default port continues to follow the configured discovery chain, while other named ports connect directly to that port on the root service instead of failing. Upstreams that do not name a port resolve through the default port.