How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

413,619

Total vulnerabilities in the database

Kyverno has unrestricted outbound requests in Kyverno apiCall enabling SSRF — github.com/kyverno/kyverno

Server-Side Request Forgery (SSRF)

Summary

A Server-Side Request Forgery (SSRF) vulnerability in Kyverno allows authenticated users to induce the admission controller to send arbitrary HTTP requests to attacker-controlled endpoints.

When a ClusterPolicy uses apiCall.service.url with variable substitution (e.g. {{request.object.*}}), user-controlled input can influence the request target. The Kyverno admission controller executes these requests from its privileged network position without enforcing any validation or network restrictions.

The issue becomes non-blind SSRF, as response data from internal services can be reflected back to the user via admission error messages.

Details

Kyverno supports variable substitution in apiCall.service.url, a documented feature intended to enable dynamic external lookups during admission control.

However, the current implementation lacks fundamental safeguards in the HTTP execution path:

Missing protections

No URL validation
User-controlled input is directly embedded into the request URL without validation or normalization.
No IP filtering
Requests can target:
- Loopback (127.0.0.1)
- Link-local (169.254.0.0/16)
- Cloud metadata services (e.g. AWS IMDS)
- Internal ClusterIP services
Redirect handling not restricted
The Go HTTP client uses default redirect behavior (CheckRedirect == nil), allowing up to 10 redirects without re-validation of the target.
Response data reflection in admission errors
Response bodies are propagated back to the user in admission responses under certain conditions.

The vulnerability is non-blind through two mechanisms:

Non-2xx responses
Response body is returned in admission error messages (e.g. executor.go:98-101)
2xx responses with non-JSON content
Parsing failures (JSON/JMESPath) include response snippets in error output

This allows attackers to retrieve data from internal services directly via kubectl output.

PoC

Preconditions

A ClusterPolicy using:

apiCall:
  service:
    url: &quot;http://{{ request.object.metadata.annotations.target }}&quot;

An authenticated user able to create matching resources (e.g. Pods)

Step 1 — Create malicious resource

apiVersion: v1
kind: Pod
metadata:
  name: ssrf-test
  annotations:
    target: &quot;169.254.169.254/latest/meta-data/iam/security-credentials/&quot;
spec:
  containers:
  - name: test
    image: nginx

Step 2 — Apply resource

kubectl apply -f pod.yaml

Step 3 — Observe output

Example output:

Error from server: admission webhook &quot;kyverno&quot; denied the request:
failed to process apiCall: &lt;response body from metadata service&gt;

Variations

Internal services: http://kubernetes.default.svc
Loopback: http://127.0.0.1:8080
Redirect chains to bypass naive filters

Impact

Vulnerability class

Server-Side Request Forgery (SSRF)
Non-blind data exfiltration

Affected scope

Kubernetes clusters using Kyverno policies with apiCall.service.url and variable substitution

Impact details

Access to internal services (ClusterIP, localhost)
Access to cloud metadata endpoints (e.g. IMDSv1 → credential exposure)
Internal network reconnaissance
Multi-tenant boundary weakening

This issue can be combined with automatic ServiceAccount token forwarding (reported separately) to form a critical attack chain.

Published: Apr 14, 2026
Updated: Apr 15, 2026
GHSA: GHSA-qr4g-8hrp-c4rw
Severity: High
Exploit:
CISA KEV:

CVSS v3:

Severity: High
Score: 7.7
AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

CWEs:

CWE-918

Affected Software
References

Software	Affected versions
github.com/kyverno/kyverno	`<= 1.17.1`

https://github.com/kyverno/kyverno/security/advisories/GHSA-qr4g-8hrp-c4rw

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.