CVE-2026-4370: Juju has Improper TLS Client/Server authentication and certificate verification on Database Cluster

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.4%, percentile 34: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 34% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/juju/juju (Go) <= 0.0.0-20260401092550-1c1ac1922b57, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

A vulnerability was identified in Juju from version 3.2.0 until 3.6.19 and from version 4.0 until 4.0.4, where the internal Dqlite database cluster fails to perform proper TLS client and server authentication. Specifically, the Juju controller's database endpoint does not validate client certificates when a new node attempts to join the cluster. An unauthenticated attacker with network reachability to the Juju controller's Dqlite port can exploit this flaw to join the database cluster. Once joined, the attacker gains full read and write access to the underlying database, allowing for total data compromise.

From the GitHub advisory

Impact Any Juju controller since 3.2.0.

An attacker with only route-ability to the target juju controller Dqlite cluster endpoint may join the Dqlite cluster, read and modify all information, including escalating privileges, open firewall ports etc.

This is due to not checking the client certificate, additionally, the client does not check the server's certificate (MITM attack possible), so anything goes.

https://github.com/juju/juju/blob/001318f51ac456602aef20b123684f1eeeae9a77/internal/database/node.go#L312-L324

PoC Using the tool referenced below.

Weakness type: CWE-295, CWE-306, CWE-287, CWE-296.

Product: github.com/juju/juju (Go) · Assigned by: canonical · Published: 2026-04-01

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.41% probability of exploitation activity in the next 30 days; percentile 34.

Timeline

• 2026-04-01 — CVE record published by canonical
• 2026-04-02 — GitHub-reviewed advisory GHSA-gvrj-cjch-728p published (critical)
• 2026-04-08 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-gvrj-cjch-728p github.com
2. CVE.org record CVE-2026-4370 cve.org
3. NVD entry CVE-2026-4370 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

Critical Go advisories · Today’s Security Digest