ClickHouse CVE-2026-116366: Unauthenticated Remote Code Execution

What is CVE-2026-116366?

ClickHouse is the open-source column-store database behind a lot of modern observability, product-analytics, LLM-ops and ad-tech stacks. CVE-2026-116366 is a critical memory-safety flaw in the ClickHouse server process. The advisory says: "an unauthenticated attacker with network access to the server can execute arbitrary code." That one sentence is the whole threat model — no user, no API token, no SQL privilege, just TCP reachability to any of the ClickHouse listener ports.

The root cause: integer overflow on the server-side parser

ClickHouse has not published the technical write-up and will not do so until 13 November 2026. Third-party vulnerability trackers classify it as CWE-190: Integer Overflow or Wraparound. The pattern that fits the available signals is familiar: a size or length field in an untrusted request is multiplied or added into a buffer allocation; the arithmetic overflows a 32-bit integer and wraps to a small positive value; the server allocates a tiny buffer and then writes attacker-controlled bytes past the end of it.

That is a textbook heap corruption primitive, and ClickHouse's server runs as a privileged, long-lived process with a rich attack surface of parsers, formats and query entry points, so turning the primitive into a shell is realistic rather than theoretical. CVSS's "High" attack complexity reflects the amount of ClickHouse-specific knowledge required today, not the long-term difficulty.

Which versions are affected

Unsupported 24.x and 25.x lines have no published fix. ClickHouse has not stated whether they are affected, which effectively means "assume they are, and upgrade off them." If you are still running an older line in production you have two problems — the CVE and the unsupported runtime — and the answer to both is the same: move to a supported LTS or stable.

Where ClickHouse is hiding in your estate

ClickHouse Cloud and BYOC are already patched by the vendor — no customer action required. Everything self-hosted is on you, and ClickHouse ships inside more products than you may realise:

• Observability and APM — Sentry (self-hosted), Signoz, OpenObserve, HyperDX
• Product analytics — PostHog (self-hosted), Plausible EE, June
• LLM observability — Langfuse, Opik, Phoenix (self-hosted)
• Security tooling — several SIEM and SOAR builds that use ClickHouse as the event store
• Internal data platforms — anything running the clickhouse/clickhouse-server, bitnami/clickhouse, or Altinity images

The bundled deployments are the single most common surprise. A Langfuse or PostHog upgrade in your Kubernetes cluster probably runs its own ClickHouse pod on an older tag than you expect — check the running image, not the Helm chart version.

The ports an attacker reaches

The advisory does not name a specific interface. ClickHouse's default listeners are:

• 8123/tcp — HTTP interface
• 9000/tcp — Native TCP protocol
• 8443/tcp — HTTPS interface
• 9440/tcp — Native TLS protocol

Any of them is a plausible exposure vector. Treat all four as hostile until you have confirmed network-level controls on the specific hosts. ClickHouse should never be exposed directly to the internet, and this CVE is the reminder.

Timeline

What to do in the next 72 hours

1. Inventory every ClickHouse. Include bundled deployments. Query the version with:

   clickhouse-client --query "SELECT version()"

   For Kubernetes: kubectl get pods -A -o jsonpath='{.items[*].spec.containers[*].image}' | tr ' ' '\n' | grep -i clickhouse.
2. Upgrade to patched builds. Use 26.3.62.3-lts, 26.8.36.3-lts, 26.9.27.3-stable or 26.10.3.7-stable from packages.clickhouse.com or the official clickhouse/clickhouse-server images. For bundled deployments, pin the ClickHouse sub-chart image independently of the parent chart's defaults.
3. Lock down the ports. Confirm 8123, 9000, 8443 and 9440 are blocked from the internet at the security group, firewall or NetworkPolicy. Bind the server to loopback or a private interface by setting <listen_host>127.0.0.1</listen_host> (and your private subnet) in config.xml.
4. Hunt for compromise on previously exposed hosts. Look back 30 days for: unexpected child processes spawned by clickhouse-server, new outbound connections from the ClickHouse host to unfamiliar IPs, writes to /tmp or /dev/shm followed by execution, newly scheduled cron entries or systemd units, and surges in 5xx responses on the HTTP interface.
5. Rotate adjacent secrets if any ClickHouse node was reachable from the public internet before patching: S3 keys used by table engines, Kafka SASL credentials, remote-dictionary HTTP tokens, and database passwords stored in users.xml or named-collections.

Why the 13 November deadline matters

Private patches hold the line until someone git diffs the fix against the previous release. Once the fix source is public, a competent researcher can usually locate the vulnerable function, identify the overflow condition, and build a crash within hours — and a working RCE within days. Patch windows measured in weeks after a critical pre-auth fix are not a plan; they are a bet. Close yours before 13 November 2026.

How TigerGate helps

• Container Security flags clickhouse/clickhouse-server, bitnami/clickhouse and Altinity images below the fixed versions — including the ClickHouse sidecars bundled in Langfuse, PostHog, Sentry and Opik charts.
• Server Vulnerability Monitoring fingerprints the installed ClickHouse version on every Linux host and cloud VM, prioritised by eBPF runtime-reachability so the nodes actually listening on 8123/9000 rise to the top.
• CSPM finds ClickHouse ports exposed to 0.0.0.0/0 in AWS security groups, Azure NSGs, GCP firewall rules and Kubernetes NetworkPolicies, with evidence linked back to the affected workload.
• eBPF runtime detection watches for exploitation side-effects: anomalous child processes spawned by clickhouse-server, unexpected outbound connections, writes to /tmp or /dev/shm followed by execution, and ClickHouse segfaults correlated with unusual client traffic.
• Compliance evidence maps the ClickHouse patch to SOC 2 CC7.1 vulnerability lifecycle, PCI DSS 6.3.3 (critical patch within 30 days) and ISO 27001 A.8.8 — the audit trail your next auditor will ask for.

Sources

• ClickHouse Security Advisories — CVE-2026-116366, 30 October 2026
• packages.clickhouse.com — patched builds 26.3.62.3-lts, 26.8.36.3-lts, 26.9.27.3-stable, 26.10.3.7-stable
• CVE-2026-116366 at NVD (pending)