リリース

Envoy v1.38.3 is a security-only release patching 15 CVEs plus one upstream wasmtime CVE. Two issues are rated critical: a TLS SAN NUL-byte auth bypass (CVE-2026-47778) and HTTP/3-to-HTTP/1 request smuggling (CVE-2026-48743); the remaining 13 are rated high, covering crashes, a zip-bomb DoS, a PKCE padding oracle, a 65 KB upstream data spillover, and a heap buffer overflow.

• securityCRITICAL: TLS SAN NUL-byte auth bypass (CVE-2026-47778)

  CVE-2026-47778 (GHSA-f8x4-rw5x-f3r7): a NUL byte embedded in a TLS SAN causes truncation during comparison, allowing an attacker to bypass certificate-based authentication. Upgrade to v1.38.3 unconditionally.

• securityCRITICAL: HTTP/3 to HTTP/1 request smuggling (CVE-2026-48743)

  CVE-2026-48743 (GHSA-8phg-2h2q-jgxf): a headers-only HTTP/3 request carrying a nonzero Content-Length can be smuggled into a downstream HTTP/1 backend. Any deployment proxying HTTP/3 to HTTP/1 is affected. Upgrade to v1.38.3.

• securityHIGH: PROXY Protocol v2 upstream data spillover (CVE-2026-47692)

  CVE-2026-47692 (GHSA-wh36-hm39-mm3r): the PROXY Protocol v2 header generator leaks "skipped" TLVs, spilling up to 65 KB of attacker-controlled data into the upstream application stream. Upgrade to v1.38.3.

• breakingIntel DLB connection balancer extension removed

  The contrib extension envoy.network.connection_balance.dlb (Intel DLB connection balancer) has been disabled at the Bazel build layer in v1.38.3 due to a broken source archive. Any deployment that relied on this extension must migrate to an alternative connection balancer.

• breakingTLS certificate Brotli compression now disabled by default

  The runtime guard envoy.reloadable_features.tls_certificate_compression_brotli is now disabled by default. When off, QUIC uses zlib-only certificate compression and TCP TLS performs no certificate compression. If you depended on Brotli compression for TLS certificates, re-enable this flag explicitly after upgrading.

Envoy v1.37.5 is a security-only release fixing 15 Envoy CVEs/GHSAs and one upstream dependency CVE, with severities reaching critical. Three critical issues stand out: HTTP/3-to-HTTP/1 request smuggling, TLS SAN auth bypass via embedded NUL bytes, and a PROXY Protocol v2 spillover that puts attacker-controlled data into upstream streams. All v1.37.x deployments should upgrade without delay.

• securityCritical: HTTP/3 to HTTP/1 request smuggling (CVE-2026-48743)

  CVE-2026-48743 (GHSA-8phg-2h2q-jgxf): HTTP/3 requests with headers-only and a nonzero Content-Length can smuggle requests into HTTP/1 upstream connections. Applies to any deployment terminating HTTP/3 and proxying to HTTP/1 backends. Upgrade immediately.

• securityCritical: TLS SAN NUL-byte auth bypass (CVE-2026-47778)

  CVE-2026-47778 (GHSA-f8x4-rw5x-f3r7): A TLS SAN containing an embedded NUL byte is truncated at that byte during comparison, allowing a certificate to match patterns it should not. Any deployment making auth decisions based on TLS SAN validation is affected. Upgrade immediately.

• securityCritical: PROXY Protocol v2 TLV spillover into upstream stream (CVE-2026-47692)

  CVE-2026-47692 (GHSA-wh36-hm39-mm3r): The PROXY Protocol v2 header generator emits TLVs that were supposed to be skipped, spilling up to 65 KB of attacker-controlled data into the upstream application stream. Affects deployments that generate PROXY Protocol v2 headers toward upstreams. Upgrade immediately.

• securityHigh: Two OAuth2 filter vulnerabilities (padding oracle + UAF)

  CVE-2026-47775 and CVE-2026-48090 (GHSA-396h-jpq4-vc7p, GHSA-3cj2-c63f-q26f): The OAuth2 filter has a PKCE code-verifier padding oracle and a use-after-free risk when an async token fetch completes after stream teardown. Both affect deployments using envoy.filters.http.oauth2.

• securityHigh: HTTP/3 QPACK blocked-decoding DoS (GHSA-p7c7-7c47-pwch)

  HTTP/3 QPACK blocked decoding (GHSA-p7c7-7c47-pwch) can be exploited to cause a DoS against the HTTP/3 stack. Affects any deployment serving HTTP/3.

• securityHigh: grpc_stats filter segfault on Connect protocol (CVE-2026-47204)

  CVE-2026-47204 (GHSA-3jxh-8p6x-7pf6): The grpc_stats filter segfaults on Connect-protocol requests routed to direct_response routes. Affects deployments using envoy.filters.http.grpc_stats.

• breakingIntel DLB connection balancer contrib extension disabled at build time

  The envoy.network.connection_balance.dlb contrib extension (Intel DLB connection balancer) has been disabled at the Bazel build layer across all platforms due to a source archive breakage. Deployments relying on this extension must pursue a local workaround or alternative balancing strategy until the source issue is resolved.

Envoy v1.36.9 is a security-only release patching 15 CVEs (2 rated critical, the rest high or medium) across TLS SAN handling, HTTP/3, PROXY protocol, JSON parsing, OAuth2, ext_proc, grpc_stats, zstd, DNS, and statsd. Operators should upgrade immediately, as two of the vulnerabilities -- TLS SAN auth bypass and HTTP/3 request smuggling -- are unconditional or broadly exploitable.

• securityCRITICAL: TLS SAN NUL-byte auth bypass (CVE-2026-47778 / GHSA-f8x4-rw5x-f3r7)

  A TLS SAN containing an embedded NUL byte causes the SAN to be truncated, bypassing certificate-based authentication checks. All deployments are affected. Upgrade to v1.36.9 immediately.

• securityCRITICAL: HTTP/3-to-HTTP/1 request smuggling (CVE-2026-48743 / GHSA-8phg-2h2q-jgxf)

  A headers-only HTTP/3 request with a nonzero Content-Length can be smuggled into HTTP/1 backends, enabling request smuggling attacks. Affects any deployment proxying HTTP/3 to HTTP/1 backends.

• securityHIGH: PROXY Protocol v2 upstream data spillover (CVE-2026-47692 / GHSA-wh36-hm39-mm3r)

  PROXY Protocol v2 header generation leaks up to 65 KB of attacker-controlled data into the upstream application stream via improperly emitted TLVs. Affects deployments using the PROXY Protocol v2 header generator.

• securityHIGH: Stack overflow on deeply nested JSON (CVE-2026-48042 / GHSA-f24p-rxw2-g6pv)

  Deeply nested JSON input triggers a stack overflow in the object destructor, crashing the proxy. All deployments are affected.

• securityHIGH: wasmtime dependency CVE (CVE-2026-47261)

  The wasmtime dependency was bumped to resolve CVE-2026-47261. All deployments using Wasm extensions are affected.

• breakingDLB connection balancer extension disabled (capability removed)

  The contrib Intel DLB connection balancer extension (envoy.network.connection_balance.dlb) is now disabled at the Bazel layer for all platforms due to a source archive breakage. Builds that previously enabled this extension will lose it silently.

Envoy v1.35.13 is a major security release fixing 13 CVEs, two of them critical: a PROXY protocol v2 TLV spillover leaking up to 65KB into the upstream stream, and a TLS SAN NUL-truncation bug that can bypass certificate-based auth. It also disables the contrib Intel DLB connection balancer extension due to a build breakage.

• securityPROXY Protocol v2 TLV spillover (CVE-2026-47692)

  Applies to all v1.35.13 deployments running PROXY protocol v2 header generation upstream. CVE-2026-47692 lets an attacker's "skipped" TLVs leak up to 65KB into the upstream application stream. Upgrade immediately if you use this feature.

• securityTLS SAN NUL truncation enables auth bypass (CVE-2026-47778)

  Applies to deployments validating client certificates by SAN. CVE-2026-47778 lets an embedded NUL byte in a TLS SAN truncate the parsed name, allowing certificates to match unintended hostnames and bypass authentication. Upgrade immediately.

• security11 more high-severity CVEs across core filters and HTTP/3

  Eleven additional high-severity CVEs are fixed across ext_proc, router internal redirects, OAuth2 (two separate issues: padding oracle and a use-after-free from late async token completion), zstd decompression, grpc_stats, JSON parsing, the DNS filter, HTTP/3 (content-length validation and a separate QPACK-based DoS), and TcpStatsdSync. Each is a crash, DoS, or memory-safety bug tied to a specific filter or codec; upgrade to pick up all fixes, or check which filters you run to prioritize.

• securityWasmtime dependency bump fixes CVE-2026-47261

  A separate wasmtime CVE (CVE-2026-47261) is fixed by bumping the com_github_wasmtime dependency. Applies to deployments using the Wasm filter.

• breakingIntel DLB connection balancer extension disabled

  The contrib extension envoy.network.connection_balance.dlb (Intel DLB connection balancer) is disabled at the Bazel build layer for all builds and platforms due to a source archive breakage. Anyone building Envoy with this extension enabled needs an alternate connection balancer.

Envoy v1.38.2 is a small patch release: one RTDS runtime bug fix and two opt-in HTTP/2 cookie observability features. No security fixes.

• breakingRTDS runtime guard fix changes delete behavior — verify your override logic

  If your config management deletes RTDS runtime guard overrides expecting them to revert to default, prior behavior was broken and left stale values. After upgrading to v1.38.2, deletes will now correctly restore defaults. Test any automation that removes runtime overrides to confirm it behaves as intended.

• enhancementUse new HTTP/2 cookie size limit to guard against oversized headers

  The new envoy.reloadable_features.http2_max_cookies_size_in_kb flag lets you cap the reassembled cookie header size in HTTP/2. If your deployment handles untrusted upstream or downstream traffic with large cookie headers, set an explicit limit to reduce memory pressure. The default is unlimited, so this is opt-in.

Envoy v1.37.4 is a small patch with one RTDS bug fix and two opt-in HTTP/2 cookie-related observability/safety features. No security CVEs.

• breakingRTDS override deletion behavior changed — verify runtime guard state

  If your deployments rely on RTDS to manage runtime guard overrides, the old behavior left stale override values after deletion. The fix now restores the process-wide default. Check that your expected default values are actually what you want after an override is removed, especially if you were working around the old broken behavior.

• enhancementUse the new cookie size limit to protect against oversized cookie headers

  HTTP/2 reassembled cookie headers had no size cap before this release. If you proxy untrusted HTTP/2 clients, set envoy.reloadable_features.http2_max_cookies_size_in_kb to a reasonable limit (e.g., 32–64 KB) to prevent unexpectedly large cookie payloads from reaching upstreams. The default remains unlimited, so this requires an explicit opt-in.

• enhancementEnable HTTP/2 header histograms in staging to baseline your traffic

  The new envoy.reloadable_features.http2_record_histograms flag adds histograms for header count, map byte size, and cookie metrics. These are useful for understanding HTTP/2 header pressure in your fleet. Enable in a non-production environment first — note these metrics will be removed in a future Envoy release, so don't build long-term dashboards around them.

Envoy v1.36.8 is a minor patch with one bug fix and two opt-in HTTP/2 observability features. No breaking changes or CVEs.

• breakingHTTP/2 header histograms are temporary — don't build dashboards on them

  The new http2_record_histograms feature and its runtime guard are explicitly scheduled for removal in a future Envoy release. If you enable them for debugging HTTP/2 header issues, treat the resulting metrics as short-lived. Don't wire them into permanent dashboards or alerts that would break on upgrade.

• enhancementEnable HTTP/2 header histograms if you're debugging large header or cookie payloads

  If you're seeing unexpectedly large HTTP/2 requests or cookie-related issues, flip envoy.reloadable_features.http2_record_histograms to get histograms on header entry count, byte size, and cookie metrics. Pair this with envoy.reloadable_features.http2_max_cookies_size_in_kb to enforce a hard cap on reassembled cookie header size — useful if you need to protect upstream services from oversized cookie headers.

Envoy v1.35.12 is a minor patch with one runtime bug fix and two opt-in HTTP/2 cookie/header observability features. No breaking changes or CVEs.

• breakingRTDS override deletion behavior changed — verify runtime guard defaults

  If you rely on RTDS to manage runtime guard overrides, test this fix in staging. Previously, deleting an override left the old value active; now it resets to the process default. Any automation that deleted overrides expecting them to persist will behave differently.

• enhancementUse the new HTTP/2 cookie size limit to guard against oversized cookie headers

  The new envoy.reloadable_features.http2_max_cookies_size_in_kb flag is off by default. If your deployments accept untrusted HTTP/2 traffic, consider setting a reasonable limit to bound memory usage from reassembled cookie headers. Pair it with the new histograms to first measure your actual cookie sizes before choosing a cap.

v1.38.1 is a security-focused patch addressing two HTTP/2 CVEs and two oauth2 vulnerabilities — upgrade immediately if running HTTP/2 or oauth2 filter.

• securityPatch HTTP/2 and oauth2 CVEs now — don't wait for your next maintenance window

  Two HTTP/2 CVEs (cookie-bomb memory exhaustion via HPACK and nghttp2 CVE-2026-27135) plus two oauth2 bugs (timing oracle and a crash-as-auth-bypass) make this a must-apply patch. If you're running the oauth2 filter, the HMAC timing side-channel is particularly nasty — attackers could probe HMAC secret validity over time. Upgrade to v1.38.1 immediately. The new HTTP/2 header limit behavior is enabled by default; only revert with `envoy.reloadable_features.http2_include_cookies_in_limits` if you have a specific, documented reason.

• breakingUpstream failure reason stripped from HTTP response bodies — check your client error handling

  Any downstream client or API consumer that parses or displays the upstream transport failure reason from the HTTP response body will now get nothing. The information is still in access logs. Audit your clients and dashboards before upgrading — if something depends on that response body content, you have a short window to either update the client or re-enable the old behavior with `envoy.reloadable_features.hide_transport_failure_reason_in_response_body`.

• breakingEDS batch LB rebuild coalescing is now opt-in — test under high-churn service discovery

  Load balancer rebuild coalescing during EDS batch host updates is disabled by default. Environments with large EDS clusters and frequent host churn (e.g., Kubernetes rolling deployments with many pods) may see increased CPU from more frequent LB rebuilds. Benchmark your control-plane interaction patterns after upgrading. Re-enable the old behavior with `envoy.reloadable_features.coalesce_lb_rebuilds_on_batch_update` if you observe performance regression.

v1.37.3 is a security-focused patch fixing two HTTP/2 CVEs and oauth2 vulnerabilities — upgrade immediately if you use HTTP/2 or oauth2 filter.

• securityPatch HTTP/2 deployments now for CVE-2026-47774 and CVE-2026-27135

  Two HTTP/2 CVEs are fixed in this release. CVE-2026-47774 enables a cookie-bomb attack that causes excessive memory usage by sending large numbers of cookies that bypass header size limits before this fix. CVE-2026-27135 is an nghttp2-level vulnerability. If you terminate HTTP/2 traffic, upgrade to v1.37.3 immediately. The new cookie-counting behavior is enabled by default; if it causes regressions, you can temporarily disable it with the feature flag `envoy.reloadable_features.http2_include_cookies_in_limits`, but treat that as a short-term workaround only.

• securityRotate oauth2 HMAC secrets after upgrading

  The timing side-channel in HMAC verification means a patient attacker could have probed whether a given secret was valid. After upgrading, rotate your oauth2 HMAC secrets as a precaution — especially in internet-facing deployments. The AES-CBC crash fix is also relevant: the previous 1/256 spurious decryption success could cause unpredictable auth behavior, not just crashes.

• breakingCookie-heavy workloads may see HTTP/2 stream resets

  The CVE-2026-47774 fix changes how cookies are counted against `mutable_max_request_headers_kb` and `max_headers_count`. Clients sending many cookies that were previously accepted may now hit limits and receive stream resets. Test your high-cookie traffic patterns in staging before rolling this to production, and review your header size limits to ensure they are set appropriately for your workloads.

v1.36.7 is a security-focused patch addressing two CVEs in HTTP/2 and an HPACK cookie-bomb attack vector in the oauth2 filter, plus a crash fix. Upgrade immediately.

• securityPatch HTTP/2 CVEs now — two CVEs affect any HTTP/2-exposed Envoy

  CVE-2026-47774 enables a cookie-bomb attack where crafted HPACK-compressed cookies inflate to exhaust Envoy memory. After patching, cookies count toward `mutable_max_request_headers_kb` and `max_headers_count`. If you see legitimate requests being reset post-upgrade, the escape hatch is the `envoy.reloadable_features.http2_include_cookies_in_limits` flag — but audit your header size limits first rather than disabling the protection. CVE-2026-27135 is an nghttp2-layer fix with no workaround; you must upgrade.

• securityAudit oauth2 filter deployments for timing and decryption exposure

  Two oauth2 bugs fixed here are subtle but serious. The timing side-channel in HMAC verification could allow an attacker to probe secret validity over many requests. The AES-CBC crash (1/256 chance on bad tokens) is a reliability issue that could be triggered deliberately. If you use the oauth2 filter with token cookies, treat this as a high-priority upgrade — there's no configuration workaround for either issue.

• breakingReview header size limits before deploying — cookie counting is a behavior change

  Cookies previously excluded from header size accounting now count toward limits. In practice, applications with many or large cookies may hit `max_headers_count` or `mutable_max_request_headers_kb` and get HTTP/2 stream resets where they didn't before. Before rolling out, check your current limit configurations against real traffic cookie sizes. If you need time, the reloadable feature flag lets you defer the behavior change, but don't leave it disabled long-term.

v1.35.11 is a security-focused patch fixing two HTTP/2 CVEs and two oauth2 vulnerabilities — upgrade immediately if you're running HTTP/2 or oauth2 filter.

• securityPatch HTTP/2 HPACK cookie-bomb vulnerability now

  CVE-2026-47774 allows an attacker to craft requests with large numbers of HPACK-compressed cookies that decompress into massive header payloads, causing excessive memory usage. The fix resets offending streams and counts cookies toward existing header size limits. Roll out this patch to any Envoy instance terminating HTTP/2 traffic. If you hit legitimate regressions with cookie-heavy workloads, the flag `envoy.reloadable_features.http2_include_cookies_in_limits` can temporarily revert the behavior — but treat that as a short-term workaround, not a solution.

• securityUpgrade if you use the oauth2 filter — two separate fixes here

  There are two distinct oauth2 issues fixed: a timing side-channel in HMAC verification (exploitable via repeated probing to determine secret validity) and a crash from incorrect AES-CBC decryption behavior on secret mismatch. The crash was probabilistic (~1/256 per request) but real. If your deployment uses Envoy's built-in oauth2 filter for token validation, this patch directly reduces both crash risk and secret exposure surface.

• enhancementEvaluate stats eviction for high-cardinality metric environments

  The new `stats_eviction_interval` config allows Envoy to periodically purge unused metrics from memory. If you're running workloads with dynamic or high-cardinality labels (e.g., per-request or per-user stats), this can meaningfully reduce memory footprint over time. Test in staging first — eviction behavior depends on whether extensions implement the evictable metrics interface, so not all metrics will be affected.

Envoy v1.38 is a massive release with several breaking changes requiring immediate action — RSA key usage enforcement, BoringSSL build flag changes, and tcp_proxy config validation are the top priorities before upgrading.

• securityPatch CVE-2026-27135 by upgrading to v1.38

  This release includes the nghttp2 patch for CVE-2026-27135, which affects HTTP/2 header field handling. If you're running Envoy as an HTTP/2 gateway or proxy, this is a direct exposure. Prioritize upgrading clusters that terminate or proxy HTTP/2 traffic. RBAC header matcher also received a fix preventing concatenation-based bypass attacks — another reason to treat this upgrade as security-relevant.

• breakingAudit TLS configs before upgrading — RSA key usage now enforced

  enforce_rsa_key_usage defaults to true starting this release and will be removed entirely next release, making it permanent. Any upstream TLS connection where the certificate's key usage doesn't match the negotiated cipher will be rejected. Before upgrading, audit your upstream certificate configurations. Test in staging first — silent failures in prod will be connection resets, not helpful error messages.

• breakingUpdate BoringSSL FIPS build pipelines before building v1.38

  The --define=boringssl=fips Bazel flag is gone. CI/CD pipelines or Dockerfiles that build Envoy with FIPS mode will fail silently or error out. Replace with --config=boringssl-fips. If you're consuming official binaries rather than building from source, this doesn't affect you directly, but verify your supply-chain tooling if you maintain custom builds.

• enhancementOpenTelemetry metrics over HTTP — drop the collector sidecar

  The OTel stat sink can now push metrics directly via OTLP/HTTP without requiring a collector sidecar. If you're running otel-collector as a DaemonSet purely for Envoy metrics forwarding, you can simplify that architecture. Evaluate whether direct OTLP/HTTP export to your backend (Grafana Cloud, Honeycomb, etc.) reduces operational overhead in your environment.

Envoy v1.37.2 is a patch release fixing three runtime bugs: a crash on listener removal, incomplete body forwarding in dynamic module filters, and a request hang on buffer overflow during internal redirects.

• breakingUpgrade immediately if using process-level access log rate limiting

  If your Envoy config uses a process-level access log rate limiter and you perform any listener hot-reload or removal, you are hitting a crash path. This is not a low-probability edge case — listener removal happens during routine config updates via xDS. Upgrade to v1.37.2 before your next config push.

• breakingCheck dynamic module filter pipelines for body truncation

  If you run dynamic module filters alongside other filters that buffer request or response bodies (e.g., ext_proc, gRPC transcoding, JWT body inspection), you may have been forwarding truncated payloads upstream or to clients without any error. Audit logs for unexpected body size mismatches and validate behavior in staging after upgrading.

• breakingInternal redirect with large request bodies could hang — patch this now

  Any route config using internal redirects combined with upstream services that can trigger redirects on large POST/PUT bodies is a hang risk. The request stalls rather than returning an error, which means your upstream timeout is the only safety net. This is a silent reliability failure. Upgrade and consider temporarily tightening request buffer limits on affected routes as a short-term guard.

Envoy v1.36.6 is a patch release fixing two bugs: incomplete body delivery in dynamic module filters and a request hang when internal redirect triggers buffer overflow.

• breakingUpgrade if you use dynamic module filters with buffering neighbors

  If your filter chain mixes dynamic module filters with any filter that buffers the body (e.g., ext_proc, grpc-web, or custom buffering filters), you were silently receiving incomplete bodies. This is a data-correctness bug, not just a performance issue. Upgrade to v1.36.6 immediately and validate that your dynamic modules are processing full payloads post-upgrade.

• breakingInternal redirect + buffer overflow caused indefinite request hang

  Any deployment using internal redirects where the request body can exceed the configured buffer limit was exposed to hung requests — requests that never complete and hold connections open. This is particularly dangerous under load. Upgrade now; in the interim, consider raising buffer limits or disabling internal redirects if you're seeing stuck requests.

Envoy v1.35.10 was released, but the published notes are too brief to summarize. See the original release notes for details.

Envoy v1.34.14 was released, but the published notes are too brief to summarize. See the original release notes for details.

Envoy v1.37.1 is a critical security patch addressing five CVEs including crash vulnerabilities and RBAC bypasses. Teams running production Envoy should prioritize immediate updates.

• securityApply critical CVE fixes immediately

  Five CVEs fixed including crash conditions in rate limiting and IPv6 handling, plus an RBAC bypass. Test your deployment in staging first, then schedule emergency maintenance to update production clusters within 24-48 hours.

• enhancementReview OAuth2 and ext_authz configurations

  If you use OAuth2 refresh tokens, verify host header behavior works correctly after the fix. For ext_authz users, check that error handling now properly respects your status_on_error settings and denied response headers reach clients as expected.

• enhancementValidate ext_proc filter chains

  Multiple ext_proc filters in a chain now work correctly. If you previously avoided chaining due to bugs, test this functionality in your development environment to simplify complex processing pipelines.

Envoy v1.36.5 delivers critical security patches addressing five CVEs including crash vulnerabilities in rate limiting, RBAC bypass issues, and memory corruption bugs that require immediate upgrading.

• securityUpgrade immediately for critical crash fixes

  Multiple CVEs can cause Envoy crashes or memory corruption. The rate limiting crash (CVE-2026-26330) and IPv6 address handling bug (CVE-2026-26310) pose immediate availability risks. Schedule emergency maintenance windows to deploy this patch, especially if you use rate limiting or handle IPv6 traffic.

• securityReview RBAC policies for multivalue header bypass

  CVE-2026-26308 allowed bypassing RBAC rules through multivalue headers. After upgrading, audit your RBAC configurations to ensure they weren't exploited and verify that header-based access controls work as expected in your environment.

• enhancementTest OAuth2 workflows after host rewriting fix

  The OAuth2 refresh bug fix changes how host headers are handled during authentication flows. If you use Envoy for OAuth2 with custom host rewriting rules, test your authentication workflows thoroughly after upgrading to ensure tokens refresh correctly.

Envoy v1.35.9 delivers critical security patches for four CVEs affecting RBAC, IPv6 handling, JSON processing, and HTTP decoding, plus OAuth2 host rewriting fixes.

• securityUpgrade immediately for critical security fixes

  Four CVEs fixed in this release could lead to authentication bypass, crashes, and memory corruption. Schedule immediate deployment especially if using RBAC policies, IPv6 networking, JSON processing, or experiencing downstream connection resets. Test thoroughly in staging first as security fixes can affect request handling behavior.

• enhancementValidate OAuth2 host rewriting behavior

  OAuth2 refresh requests now correctly preserve original Host headers instead of being overridden. If your setup relies on custom host rewriting for OAuth2 flows, verify that authentication still works as expected after upgrading. This change improves compliance with OAuth2 specifications.

Critical security patch addressing four CVEs including RBAC bypass, IPv6 crash, memory corruption, and HTTP decode vulnerabilities that require immediate upgrade.

• securityUpgrade immediately for RBAC bypass fix

  CVE-2026-26308 allows attackers to bypass RBAC policies using multivalue headers. This directly impacts access control security. Schedule emergency maintenance to upgrade all Envoy instances, especially those using RBAC for authorization.

• securityPatch IPv6 crash vulnerability in production

  CVE-2026-26310 causes crashes when processing scoped IPv6 addresses, leading to service disruption. If you handle IPv6 traffic or run dual-stack configurations, prioritize this upgrade to prevent potential DoS attacks.

• securityAddress JSON processing memory corruption

  CVE-2026-26309 corrupts string null terminators during JSON processing, potentially leading to memory corruption or information disclosure. Update immediately if your services process JSON payloads through Envoy.