CVE-2026-39429Public exploitNetwork attack vector

Unauthenticated cache reads and writes via pre-mux routing

Published Apr 8, 2026 · Updated Apr 8, 2026

Missing authentication and authorization in kcp before 0.29.3 and 0.30.0 through 0.30.2 allows remote attackers to read or write cache data. The root shard's preHandlerChainMux proxies /services/cache/ requests from the pre-mux chain before authentication and authorization handlers run. Exposure requires a root shard reachable without a filtering front proxy; reads disclose replicated resources, while writes are short-lived and require a sub-second race for privilege escalation.

CVSS severity8.2
High
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing authentication and authorization in kcp before 0.29.3 and 0.30.0 through 0.30.2 allows remote attackers to read or write cache data. The root shard's preHandlerChainMux proxies /services/cache/ requests from the pre-mux chain before authentication and authorization handlers run. Exposure requires a root shard reachable without a filtering front proxy; reads disclose replicated resources, while writes are short-lived and require a sub-second race for privilege escalation.

The record

CVE
CVE-2026-39429
Published
Apr 8, 2026
Updated
Apr 8, 2026
Vendor
kcp
Product
kcp
Classifications
CWE-302, CWE-862, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.29.3
  2. Affected versionversion=>= 0.30.0, < 0.30.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

kcp · kcpversion=< 0.29.3; version=>= 0.30.0, < 0.30.3

Published CVSS scores

9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
8.2GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-302Authentication Bypass by Assumed-Immutable Data
CWE-862Missing Authorization
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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