Releases

NATS server v2.14.3 is a maintenance release dominated by JetStream, MQTT and clustering bug fixes, with two MQTT fixes closing pre-auth memory exhaustion and panic conditions and one breaking change: JSONP monitoring support has been removed.

• securityMQTT memory exhaustion and panic fixes

  Applies to servers exposing MQTT. Fixed in v2.14.3: malformed partial CONNECT packets could exhaust pre-auth memory, and a PUBLISH remaining-length underflow could panic the server. Upgrade if you run MQTT, especially with untrusted or public clients.

• breakingJSONP monitoring support removed

  Applies to deployments relying on JSONP callbacks against monitoring endpoints (e.g. /varz, /connz via callback= param). This is removed in v2.14.3; switch dashboards or scripts to plain JSON polling before upgrading.

• breakingPermission checks tightened for leaf trace destination and NoAuthUser

  Applies to leaf node setups using Nats-Trace-Dest, and to accounts using NoAuthUser. Fixed in v2.14.3: leaf connections could bypass Nats-Trace-Dest publish permission checks, and NoAuthUser did not enforce connection restrictions. Review permission and NoAuthUser configs after upgrading, since previously permitted traffic may now be denied as intended.

v2.12.12 is a bugfix and hardening release for nats-server, centered on numerous JetStream/Raft data-integrity and panic fixes plus removal of JSONP support from monitoring endpoints. No CVEs are disclosed, but several fixes close memory-exhaustion and panic paths reachable via malformed MQTT input that operators should treat as security-relevant.

• securityMQTT partial-CONNECT and PUBLISH-underflow crash/DoS fixes

  If you run MQTT, upgrade to fix two memory-exhaustion/panic paths: partial CONNECT packets could exhaust pre-authentication memory, and PUBLISH remaining-length underflow could panic the server. Both are exploitable by unauthenticated clients sending malformed input.

• securityInteger-overflow panics fixed in monitoring and JetStream usage tracking

  CONNZ/SUBSZ pagination previously could panic on integer overflow, and JetStream remote usage updates could panic on length integer overflow. Operators with large clusters or heavy monitoring polling should upgrade to remove these panic-inducing edge cases.

• breakingJSONP support removed from monitoring endpoints

  JSONP callback support has been removed from monitoring endpoints in v2.12.12, unconditionally. Any tooling or dashboards that rely on JSONP callbacks against /varz, /connz, or similar endpoints will break and must switch to plain JSON requests.

NATS v2.12.11 is a single-fix patch release targeting a JetStream regression in v2.12.7 that caused stale subject state tracking and 'Message Not Found' errors on streams with per-subject message limits.

• breakingUpgrade if you use max-messages-per-subject on any stream

  If you run NATS 2.12.7–2.12.10 and have streams configured with MaxMsgsPerSubject (max_msgs_per_subject), you are exposed to silent stale-state bugs that surface as 'Message Not Found' errors. These errors can cause consumers to miss messages or behave unpredictably. Upgrade to 2.12.11 immediately. If you are already on 2.14.x, you are not affected and no action is needed.

NATS v2.14.2 is a focused stability release fixing multiple JetStream data integrity issues, lock release bugs, and protocol corruption risks — upgrade if you run JetStream at any meaningful scale.

• securityProtocol corruption vectors closed — critical for WebSocket and JetStream users

  Two protocol corruption bugs were fixed: one in $JS.ACK subject rewriting and one in compressed WebSocket client buffer handling. Either could produce malformed frames that corrupt stream state or client sessions. If you expose NATS WebSocket endpoints or rely heavily on JetStream ACKs, treat this as a security-adjacent stability issue and prioritize the upgrade.

• breakingTwo separate lock-release bugs can cause silent hangs — patch now

  Both the filestore and consumer code paths had cases where locks were never released after specific error conditions (write errors and start sequence errors). In production this means stuck consumers or hung filestore operations that don't recover without a restart. If you've seen unexplained JetStream stalls, this is likely why. Upgrade to v2.14.2 immediately.

• enhancementHigh subject-count streams no longer risk CPU spikes — no config change needed

  The filestore block skip check was triggering runaway CPU on streams with very high subject counts. The fix is automatic after upgrade — no configuration changes required. If you've been working around this with stream design compromises (e.g., artificially limiting subjects per stream), you can revisit those decisions after upgrading.

v2.12.10 is a focused bug-fix release addressing protocol corruption risks, JetStream Raft/quorum issues, and a CPU runaway bug in high-cardinality streams.

• securityUpdate x/crypto and nkeys immediately

  This release bumps golang.org/x/crypto to v0.52.0 and nkeys to v0.4.16. These libraries handle cryptographic operations in NATS auth flows. Don't wait for scheduled maintenance — patch now, especially if your clusters are internet-exposed or use decentralized auth.

• breakingProtocol corruption fixes require prompt upgrade for WebSocket and JetStream users

  Two separate protocol-level corruption bugs are fixed here: one in compressed WebSocket clients, one in $JS.ACK subject rewriting. Either can silently corrupt message framing. If you run WebSocket clients or any JetStream workload with acknowledgements, staying on 2.12.9 or earlier is a real risk. Upgrade servers first, then clients.

• enhancementHigh-cardinality JetStream streams get a CPU safety fix — verify your config

  The block skip check on streams with very high subject counts could cause runaway CPU. That check is now disabled for those cases. If you've been seeing unexpected CPU spikes on JetStream nodes with streams containing millions of subjects, this is likely the culprit. After upgrading, also review Counter stream and message schedule configs — new constraints are enforced that may reject previously accepted but incorrect configurations.

NATS v2.14.1 is a substantial patch release fixing ~30 bugs across JetStream, clustering, and core messaging — several of them data-integrity and panic-level issues worth deploying promptly.

• securitygolang.org/x/crypto bumped to v0.51.0 — update now if you embed nats-server

  The x/crypto and x/sys dependency updates often carry CVE fixes. If you embed nats-server as a Go library (common in edge/IoT deployments), rebuild and redeploy. For standard deployments, just upgrade the binary. Don't sit on this one — crypto library updates in a messaging server are not optional hygiene.

• breakingReview the 2.14 Upgrade Guide before deploying — 2.13.x was skipped

  The release notes explicitly reference backwards-compatibility notes against 2.12.x, not 2.13.x, because that minor version was never released. If your team is running 2.12.x and skipped 2.13.x, read the 2.14 upgrade guide carefully before rolling out. Pay attention to JetStream consumer and stream API changes that may affect your clients.

• enhancementUse the new client-traffic /varz metrics for baseline observability

  The four new metrics (in/out client msgs/bytes) give you a cleaner split between client traffic and internal cluster/leafnode chatter. Wire these into your Prometheus scrape or monitoring dashboard now to establish baselines. This is especially useful for capacity planning on servers that handle mixed client and cluster traffic, since previously you had to infer client load from total metrics.

v2.12.9 is a dense bug-fix release targeting JetStream stability — covering Raft correctness, consumer state corruption, and filestore encryption bugs that could silently corrupt data.

• securityUpdate: golang.org/x/crypto bumped to v0.51.0

  The x/crypto dependency was updated alongside Go 1.25.10. If your org tracks CVEs against transitive dependencies, verify your SBOM tooling picks this up. Upgrade to v2.12.9 to pull in the patched crypto library — there's no workaround at the application level.

• breakingEncrypted JetStream users must upgrade — filestore corruption risk

  A bug in filestore encryption mode conversion could cause block-level corruption when switching encryption settings (PR #8105, #8166). If you've ever changed encryption mode on an existing stream, inspect those streams after upgrading. If corruption already occurred, you'll need to restore from a pre-conversion snapshot.

• enhancementUse the new /varz client traffic metrics for capacity planning

  The four new metrics (in/out_client_msgs and in/out_client_bytes) let you separate actual client-facing load from internal cluster/leafnode traffic. Wire these into your Prometheus scrape now — they're directly useful for right-sizing clusters and spotting noisy clients without needing to parse per-connection data.

NATS v2.14.0 (skipping 2.13.x) brings JetStream scheduling, fast-ingest batch publishing, consumer reset API, and critical Raft data-loss fixes. Review the upgrade guide before deploying.

• breakingRead the 2.14 Upgrade Guide — 2.13.x was skipped

  This release jumps from 2.12.x to 2.14.x. The upgrade guide covers backwards compatibility breaks you must address. If you use ACLs on JetStream ACK or flow control subjects, the new domain-aware format ($JS.ACK.domain.acchash.stream.consumer.>) is disabled by default now but becomes the default in v2.15 — start updating your ACL rules now so the v2.15 upgrade isn't a fire drill.

• breakingRaft startup now fails on corrupt/missing snapshots — test your recovery procedures

  Previously, a node with a corrupt or misaligned snapshot might start silently with bad state. Now it refuses to start. This is the right behavior, but if you have any clusters with questionable disk health or have experienced unclean shutdowns, validate your snapshot integrity before rolling this upgrade out. Ensure your ops runbook covers the recovery path for this scenario.

• enhancementConsumer Reset API removes a painful operational pattern

  Rewinding a consumer previously meant deleting and recreating it — disruptive and error-prone. The new $JS.API.CONSUMER.RESET API lets you move a consumer back to an earlier sequence in place. If you maintain any tooling or runbooks that handle consumer rewind or replay scenarios, update them to use this API. It's also useful for incident recovery workflows.

NATS v2.12.8 is a substantial bug-fix release targeting JetStream stability — particularly clustered stream/consumer reliability, Raft edge cases, and a bearer JWT disclosure vulnerability in the monitoring API.

• securityPatch immediately: /connz was leaking bearer JWTs

  Any deployment using JWT-based auth with the monitoring endpoint exposed (even internally) was potentially leaking bearer tokens in /connz responses. Rotate any JWTs that may have been exposed, audit monitoring endpoint access logs, and upgrade to v2.12.8 now. If you can't upgrade immediately, restrict /connz access via firewall or NATS monitoring auth.

• securityCLI argument secrets now redacted in monitoring

  Route and cluster URLs passed as CLI arguments (which often contain credentials) were previously visible in monitoring output. Upgrade to v2.12.8 and review any monitoring dashboards or log aggregation pipelines that may have captured this data historically.

• enhancementJetStream cluster operators: test your scaling and recovery paths

  This release fixes several nasty edge cases — stream leader catch-up from snapshots, Raft commit index resets on term mismatches, in-flight assignment visibility for stream/consumer info, and the 'last sequence mismatch' error from failed proposals. If you've been seeing any of these intermittent errors in clustered JetStream, v2.12.8 is a high-priority upgrade. After upgrading, monitor for reduced error rates in stream info and consumer info endpoints during scaling operations.

NATS v2.11.17 is a security and stability patch addressing JWT bearer token exposure in monitoring endpoints, credential redaction gaps, and several crash/correctness bugs.

• securityPatch immediately: /connz was leaking bearer JWTs

  Any operator exposing the NATS monitoring port (default 8222) to internal or external networks should treat this as urgent. Bearer tokens visible in /connz could be harvested and replayed. Rotate any JWTs that may have been exposed, audit who had access to your monitoring endpoints, and upgrade to 2.11.17 now. If you cannot upgrade immediately, firewall the monitoring port.

• securityCLI-embedded secrets were visible in monitoring output

  If your NATS deployment passes route or cluster URLs with embedded credentials as command-line arguments, those secrets were previously visible in monitoring output. Audit your monitoring data for any historical exposure, rotate affected credentials, and upgrade. Long-term, prefer config files or environment-based secret injection over CLI arguments.

• breakingRepeated CONNECT behavior change may affect edge-case clients

  The fix for repeated CONNECT messages clearing subscriptions changes previously tolerated (but incorrect) behavior. Custom clients or unusual connection patterns that send multiple CONNECT messages on the same connection could see subscriptions unexpectedly dropped. Audit any non-standard client code before upgrading in production.

v2.12.7 is a targeted bug-fix release addressing ACL bypass vulnerabilities, multiple leafnode panics, a JetStream consumer stuck state, and an MQTT JWT regression from 2.12.6.

• securityPatch ACL bypass bugs immediately if you use deny rules or queue groups

  Two ACL enforcement bugs are fixed here. Overlapping wildcard patterns in deny ACLs were not enforced correctly, and queue subscriptions could bypass non-queue deny rules entirely. If your security model relies on deny-based ACLs — especially with wildcards or mixed queue/non-queue subscribers — treat this as a must-upgrade. Audit your ACL configurations after upgrading to confirm expected deny behavior is active.

• breakingMQTT users on 2.12.6 must upgrade — auth callout JWT was broken

  If you deployed 2.12.6 with MQTT clients using auth callout, JWTs were not being forwarded to the callout service, meaning your auth logic was silently bypassed or failing. This regression is fixed in 2.12.7. Upgrade immediately and verify MQTT client authentication is functioning end-to-end.

• enhancementmax_mem_store and max_file_store can now be increased via config reload

  You can now raise JetStream storage limits without restarting the server — just update the config and reload. Decreasing is still not supported via reload. Useful for capacity adjustments during peak periods without downtime. Plan your storage sizing with headroom so you can expand reactively if needed.

v2.11.16 is a security-focused patch fixing multiple ACL bypass vulnerabilities in queue subscriptions, leafnode inbound messages, and wildcard deny patterns — update immediately if you rely on NATS authorization.

• securityACL bypass via queue subscriptions — patch now

  Queue subscribers could silently bypass deny rules intended for non-queue subscriptions. If your authorization model uses deny patterns to restrict subjects, those controls were not reliably applied. Audit your ACL configurations and update to v2.11.16 before anything else. This affects any multi-tenant or permission-isolated NATS deployment.

• securityLeafnode ACL enforcement was incomplete — verify your leaf configs

  Inbound messages on leafnode connections were not always checked against ACL permissions. If you run leafnode-connected clusters with per-account or per-user authorization, treat this as a potential unauthorized data access vector. After upgrading, review leafnode user credentials and their associated permission sets.

• breakingno_auth_user scope change may affect existing setups

  The no_auth_user option is now restricted to client connections only. If you had any tooling or configuration relying on no_auth_user applying to leafnode or other non-client connection types, those connections will now require explicit credentials. Test in staging before rolling this update to production leafnode infrastructure.

v2.12.6 is a critical security release fixing 11 CVEs across MQTT, JetStream, WebSockets, leafnodes, and mTLS. Also fixes a JetStream regression from 2.12.5 that could lose consumer assignments.

• securityUpgrade immediately — 11 CVEs patched across core subsystems

  This release patches CVEs in MQTT (3), JetStream (2), leafnodes (2), WebSockets (1), mutual TLS (1), command-line credentials (1), and publish permissions (1). If you run any of these features in production, there is no safe reason to stay on an older build. Review your deployment against the affected subsystems and prioritize accordingly — MQTT and leafnode users face the highest exposure count.

• breaking1MB JWT size limit is now enforced

  JWTs larger than 1MB will be rejected. This is unlikely to affect most deployments, but if you use deeply nested or unusually large account/user JWTs (e.g., with large permission sets), validate your JWT sizes before upgrading. Check your operator's JWTs and any dynamically issued credentials.

• breakingJetStream consumer assignments could be silently lost on 2.12.5 — fix requires upgrade

  A regression in 2.12.5 caused stream updates on clustered JetStream with async snapshots to drop consumer assignments. If you're running 2.12.5 with clustered JetStream, audit your consumer counts before and after upgrading to confirm no silent data loss occurred. This is the most operationally dangerous bug in this release cycle.

v2.11.15 is a critical security release patching 11 CVEs across MQTT, leafnodes, WebSockets, JetStream, and mTLS. Upgrade immediately if you run any of these features.

• securityUpgrade now — 11 CVEs, multiple remote attack surfaces

  This release patches CVEs across nearly every major NATS feature area. MQTT users face the most exposure: password leakage in monitoring endpoints, session hijacking via mismatched client IDs, and malformed packet panics. WebSocket deployments had an unbounded memory allocation path exploitable for DoS. Leafnode and mTLS users also have targeted fixes. There is no safe reason to delay this upgrade. Pin your deployments to v2.11.15 and roll it out across all clusters — dev, staging, and production.

• breakingMQTT client ID restrictions may break existing clients

  NATS special characters (`.`, `>`, `*`, spaces, tabs) are now rejected in MQTT client IDs. If any of your MQTT clients use these characters — common in some IoT device naming schemes — they will fail to connect after upgrade. Audit your MQTT client ID naming conventions before rolling out this version in production. Also verify that your MQTT clients do not rely on the previously broader implicit permission scope, which is now restricted to `$MQTT.sub.*` and `$MQTT.deliver.pubrel.*` prefixes.

• enhancementTrace logging and monitoring endpoints now redact secrets

  Command-line secrets were previously visible in expvar monitoring output and trace logs. This is fixed. If you've been scraping the monitoring port or collecting trace logs and routing them to external systems (log aggregators, SIEM, etc.), check whether any historical data needs to be rotated or scrubbed. Going forward, no additional config is needed — redaction is automatic.

NATS v2.12.5 delivers critical security fixes for leafnode compression and WebSocket vulnerabilities, while significantly improving JetStream backup performance and fixing numerous stability issues in filestore operations.

• securityUpdate immediately for critical CVE fixes

  Two CVEs affect production systems: CVE-2026-29785 impacts leafnode compression and CVE-2026-27889 affects WebSocket connections. Both can cause server panics or security issues. Schedule maintenance window to update all NATS servers running v2.12.4 or earlier.

• enhancementOptimize JetStream backups for unreliable networks

  Stream backups now support window_size parameter for better flow control. If you run backups over slow or unreliable connections, configure appropriate window sizes to improve throughput and reduce backup failures. Test with your network conditions to find optimal values.

• enhancementReview async metalayer snapshot behavior

  Metalayer snapshots now run asynchronously to prevent blocking JS API operations. This improves performance but changes timing behavior. If your applications rely on synchronous snapshot timing, set `meta_compact_sync: true` in jetstream config block to restore previous behavior.

NATS v2.11.14 is a critical security release addressing two CVEs affecting leafnode compression and WebSocket features, plus multiple stability fixes to prevent server panics.

• securityUpgrade immediately if using leafnodes or WebSockets

  Two CVEs affect common NATS configurations. If you have leafnode compression or WebSocket features enabled, upgrade immediately to prevent potential security exploits. Check your configuration for 'compression: enabled' in leafnode sections or 'websocket' listeners.

• securityReview WebSocket Origin validation settings

  Origin header validation now includes protocol scheme verification. Audit your WebSocket client configurations to ensure they specify correct origins (including https:// or wss:// schemes) to avoid connection rejections after upgrade.

• enhancementMonitor for reduced panic incidents

  This release fixes multiple panic conditions in leafnode and WebSocket handling. After upgrading, you should see fewer unexpected server restarts. Review your monitoring dashboards to confirm improved stability metrics.