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.

326,895

Total vulnerabilities in the database

CVE-2026-30858

Summary

A DNS rebinding vulnerability in the web_fetch tool allows an unauthenticated attacker to bypass URL validation and access internal resources on the server, including private IP addresses (e.g., 127.0.0.1, 192.168.x.x). By crafting a malicious domain that resolves to a public IP during validation and subsequently resolves to a private IP during execution, an attacker can access sensitive local services and potentially exfiltrate data.

Details

The vulnerability exists because the web_fetch tool lacks complete DNS pinning. The application performs URL validation only once via validateParams(), but the URL is then passed unchanged to the fetchHTMLContent() function, which eventually reaches fetchWithChromedp(). The headless browser (Chromedp) resolves the hostname independently without DNS pinning, allowing a time-of-check-time-of-use (TOCTOU) attack.

Validation phase (first DNS resolution):

if err := t.validateParams(p); err != nil {
    // Returns error for private IPs
    results[index] = &amp;webFetchItemResult{
        err: err,
        // ...
    }
    return
}

Execution phase (second DNS resolution): The original URL (not the resolved IP) is passed through the execution chain:

output, data, err := t.executeFetch(ctx, p)
// Calls fetchHTMLContent(ctx, targetURL) where targetURL is the original hostname

Chromedp execution (vulnerable DNS resolution):

func (t *WebFetchTool) fetchWithChromedp(ctx context.Context, targetURL string) (string, error) {
    // targetURL is not DNS-pinned; browser resolves it independently
    err := chromedp.Run(ctx,
        chromedp.Navigate(targetURL),  // Third DNS lookup occurs here
        chromedp.WaitReady(&quot;body&quot;, chromedp.ByQuery),
        chromedp.OuterHTML(&quot;html&quot;, &amp;html),
    )
}

The attacker controls a domain that can be configured to return different DNS responses to different queries, enabling them to bypass the initial private IP check and access restricted resources during the actual fetch.

PoC

Setup:

Deploy the DNS rebinding server (attached Python file) with the following systemd configuration:

[Unit]
Description=DNS Rebinding Test Server
After=network.target

[Service]
Type=simple
User=root
WorkingDirectory=/root/Repos/dns-rebinding-server
ExecStart=/root/.proto/shims/python -u /root/Repos/dns-rebinding-server/server.py --token aleister1102 --domain aleister.ninja --port 53 --global-tracking --ip1 1.1.1.1 --ip2 0.0.0.0 --first-response-count 1 --reset-time 0
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target

This configures the DNS server to:

Return 1.1.1.1 (a public IP) for the first DNS query
Return 127.0.0.1 (localhost) for all subsequent queries
TTL is set to 0 to prevent caching

The sequence can also be reset via reset.domain.com (reset to 1.1.1.1).

> Note: We may need to reset the sequence as the TOCTOU attack is not truly reliable and needs to be triggered multiple times.

Set up a simple HTTP server on the localhost of the backend service:

python -m http.server 8888

Configure the malicious domain to point to the DNS rebinding server

Execution:

Enable web search on an agent.
Prompt the agent to fetch content from the attacker-controlled domain (e.g., http://attacker.example.com)
The sequence of events:
- First DNS query (validation phase): attacker.example.com → 1.1.1.1 ✓ Passes validation
- Second DNS query (execution phase): attacker.example.com → 127.0.0.1 ✗ Bypass achieved
- The web_fetch tool successfully connects to 127.0.0.1:8080 and returns the local server's content

Result: The attacker gains access to the local HTTP server and can read its content, demonstrating that internal resources are now accessible through the rebinding attack.

PoC video:

https://github.com/user-attachments/assets/68daaa87-4b9b-4b6e-b6f6-ee123f5fcda9

Impact

Vulnerability Type: DNS Rebinding / Server-Side Request Forgery (SSRF)

Who is impacted:

Any user or agent with web search capability can exploit this vulnerability
The vulnerability grants access to internal services, configuration files, metadata services, and other sensitive resources normally restricted to the internal network
In cloud environments, this could allow access to metadata endpoints (e.g., AWS IMDSv1) to obtain credentials and secrets\

Published: Mar 6, 2026
Updated: Mar 7, 2026
CVE: CVE-2026-30858
GHSA: GHSA-h6gw-8f77-mmmp
Severity: High
Exploit:

CVSS v3:

Severity: Unknown
Score:
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CWEs:

CWE-918

Affected Software
References

Software	From	Fixed in
github.com/Tencent/WeKnora	-	0.2.13.x

https://github.com/Tencent/WeKnora/security/advisories/GHSA-h6gw-8f77-mmmp

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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.