Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:NSummary
CVE-2026-39429 is a high-severity Authentication Bypass by Assumed-Immutable Data (CWE-302) vulnerability in Kcp Kcp. Its CVSS base score is 8.2 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 36th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to AC-24 (Access Control Decisions) and AC-25 (Reference Monitor) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-39429 is a security vulnerability in kcp, a Kubernetes-like control plane designed for form-factors and use-cases beyond Kubernetes and container workloads. In versions prior to 0.30.3 and 0.29.3, the cache server is directly exposed by the root shard without any authentication or authorization mechanisms. This flaw, linked to CWE-302 and CWE-862, enables unauthorized parties with access to the root shard to perform read and write operations on the cache server.
The vulnerability carries a CVSS v3.1 base score of 8.2 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N), making it remotely exploitable over the network with low attack complexity and no user interaction or privileges required. Any attacker able to reach the root shard endpoint can extract sensitive cached data, achieving high confidentiality impact, and make limited modifications to cache contents, resulting in low integrity impact without affecting availability.
Mitigation is available through upgrades to kcp versions 0.30.3 or 0.29.3, which address the exposure. Additional details are provided in the GitHub security advisory (GHSA-3j3q-wp9x-585p) and release notes at https://github.com/kcp-dev/kcp/releases/tag/v0.29.3 and https://github.com/kcp-dev/kcp/releases/tag/v0.30.3.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-20607
Vulnerability Data
kcp is a Kubernetes-like control plane for form-factors and use-cases beyond Kubernetes and container workloads. Prior to 0.30.3 and 0.29.3, the cache server is directly exposed by the root shard and has no authentication or authorization in place. This allows…
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anyone who can access the root shard to read and write to the cache server. This vulnerability is fixed in 0.30.3 and 0.29.3.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 5 hardening rules · 3 OS baselines
V7.2.4
Mitigating Controls (NIST 800-53 r5) AI
AC-3 directly requires enforcement of authorization decisions on every access request, structurally eliminating missing authorization checks.
AC-24 mandates that access control decisions are applied to each request, preventing bypass of authorization logic.
AC-25 requires a tamperproof, always-invoked reference monitor that ensures authorization checks cannot be omitted.
Mandates proper unique identification and authentication of users, precluding reliance on attacker-controlled immutable assumptions.
AC-6 reduces the set of actions reachable without proper authorization, limiting blast radius of missing checks.
Mandates proper identification and authentication for non-organizational users, precluding reliance on attacker-controlled immutable assumptions.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Explicitly requires defining, enforcing, and reviewing authorizations and least privilege, directly preventing missing authorization checks.
Strong authentication mechanisms directly avoid reliance on attacker-controlled immutable data.
Protecting and verifying identity assertions prevents tampering with data assumed immutable during auth.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can discover and block authentication bypasses that rely on mutable data.
Requiring authentication and credentials before any access occurs eliminates the absence of authorization checks that would otherwise allow an unauthenticated actor to reach protected resources.
Access-control policy can mandate validation of all identity data, reducing reliance on assumed-immutable fields.
Identity-management processes can require verification of mutable attributes, mitigating the root cause.
Proper management of authentication information prevents use of client-controlled tokens or cookies as sole proof of identity.
Access-rights reviews can detect and revoke rights granted via tampered immutable data.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248581 OL 8 must require users to provide a password for privilege escalation. prevents CWE-862
- V-252656 The OL 8 operating system must not be configured to bypass password requirements for privilege escalation. prevents CWE-862
RHEL 7 (2 rules)
- V-251704 The Red Hat Enterprise Linux operating system must not be configured to bypass password requirements for privilege escalation. prevents CWE-862
- V-204429 The Red Hat Enterprise Linux operating system must be configured so that users must provide a password for privilege escalation. prevents CWE-862