ClickHouse Server Unauthenticated Remote Code Execution (CVE-2026-116366)

ClickHouse describes CVE-2026-116366 as an issue that, "under certain conditions, could allow an unauthenticated user with network access to execute arbitrary code on the ClickHouse Server." It disclosed the flaw and its fixed builds on 30 October 2026. ClickHouse says the fix is already applied to all ClickHouse Cloud and BYOC deployments.

ClickHouse is its own CVE numbering authority, and its record gives a CVSS v4.0 score of 9.5, Critical. The vector is AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H. The record names CWE-190, integer overflow or wraparound, as the weakness. It lists CAPEC-248, command injection, as the impact.

What ClickHouse Has Not Disclosed

The advisory is short. It does not name the "certain conditions" or say which interface or port the attack uses. It does not say how the integer overflow leads to code execution. We do not guess at those points on this page.

When we checked the ClickHouse GitHub repository on 30 October, it had no security advisory for CVE-2026-116366. It also had no release or tag for the four fixed builds. The official Docker Hub images for all four builds were pushed on 26 October, four days before the advisory.

No Login, but High Attack Complexity

The vector says the attack needs no privileges and no user action, over the network. It also sets Attack Requirements to None. In CVSS v4.0, FIRST uses that value when the attack "does not depend on the deployment and execution conditions of the vulnerable system."

The vector does set Attack Complexity to High. FIRST's CVSS v4.0 specification uses High when the attack depends on evading "security-enhancing techniques," such as address space randomization (ASLR), or on a target-specific secret. This is our reading of the score, not a ClickHouse statement. The scored conditions point to exploit hurdles, not to a rare setup.

What the Researcher Says

The CVE record credits Elshad Toklayev with the report. On X, he made a broader claim than the advisory: unauthenticated RCE on "any @ClickHouseDB instance using just the public service hostname."

He wrote that the report went through Bugcrowd, where ClickHouse runs its bug bounty. ClickHouse has not confirmed the "any instance" wording, and its own text keeps the "certain conditions" caveat. Open the post on X (@elsh0x00, 30 October).

Earlier Pre-Login ClickHouse Flaws

This is not the first ClickHouse flaw that needs no login. The security changelog lists these:

• CVE-2024-6873: a crafted request to the native interface could redirect the server's execution flow, with no login. ClickHouse said no known proof-of-concept RCE code had been produced or exploited.
• CVE-2023-47118, CVE-2023-48298 and CVE-2023-48704: codec bugs that let an attacker with no login crash the server.

ClickHouse has not said that CVE-2026-116366 uses the native interface. The history only shows that pre-login code paths have held serious bugs before.

What Our Checks Showed

These are the public signals we checked on 30 October 2026.

We are not saying this flaw is exploited. The fixed builds have been public on Docker Hub since 26 October. Our remote code execution glossary entry explains how this class of flaw works and how to reduce the risk.

ClickHouse has also moved its bundled Brotli to 1.2.1 for the HTTP2Shell decoder flaw. It backported the change to the 26.10, 26.9, 26.8 and 26.3 branches on 25 and 26 October. Our HTTP2Shell post on the Brotli decoder flaw tracks it. The CVE-2026-116366 advisory does not mention Brotli, and ClickHouse has not said whether the two are linked.

The ClickHouse CVE record lists four affected branches of ClickHouse Server, on x86 and ARM. Each branch is affected below its fixed build. The record also sets the default status to affected, so versions it does not list are treated as affected too.

The ClickHouse security policy lists 26.10, 26.9, 26.8 and 26.3 as supported with security updates. It marks 26.4 to 26.7, and 26.2 and older, as unsupported. The changelog names no fixed build for those branches and no workaround.

ClickHouse says it applied the fix to all ClickHouse Cloud and BYOC deployments. Self-managed servers, including Docker and Kubernetes installs, are upgraded by their owners. Our ClickHouse vulnerability patch plan covers which ports to test, the order to patch in and what to log.

Our patch management entry covers how to plan and check a rollout across many nodes.