Listen to this Post
How CVE-2026-21887 Works
OpenCTI is an open-source platform for managing cyber threat intelligence knowledge and observables. Prior to version 6.8.16, the platform’s data ingestion feature accepted user-supplied URLs without performing any validation. This feature uses the Axios HTTP client with its default configuration, which includes the `allowAbsoluteUrls: true` setting. This configuration permits Axios to accept and process absolute URLs provided by the user, allowing an attacker to craft requests to arbitrary endpoints, including internal services. The vulnerability results in a semi-blind Server-Side Request Forgery (SSRF), as the attacker may not receive the full response from the internal service, but the request can still reach and potentially impact internal systems. This allows an attacker to interact with internal services that are not publicly exposed, such as Elasticsearch, Redis, or RabbitMQ, potentially extracting sensitive data or manipulating internal components. In cloud environments, the attacker could target metadata services like AWS, Azure, or GCP to obtain credentials and configuration details, which could lead to full compromise of the infrastructure. Even though the SSRF is semi-blind and the attacker may not see the full response, the ability to interact with internal services can enable enumeration, data exfiltration, and in some cases remote code execution if internal APIs expose dangerous functionality. The vulnerability is fixed in OpenCTI version 6.8.16.
DailyCVE Form
Platform: OpenCTI-Platform
Version: < 6.8.16
Vulnerability: Semi-Blind SSRF
Severity: High (7.7)
Date: 2026-03-12
Prediction: 2026-03-12 (Fixed)
What Undercode Say
Analytics
The vulnerability stems from a lack of input validation in the data ingestion feature and the use of Axios with default settings that allow absolute URLs. This combination allows an attacker to manipulate the URL parameter to point to internal resources. The CVSS score of 7.7 indicates a high severity. The attack vector is network-based, requires low privileges, and has a low attack complexity. The scope is changed, and the confidentiality impact is high. The EPSS score is very low (<1%), and the vulnerability is not listed in the KEV catalog, suggesting a low current exploitation probability. However, the potential impact is significant, especially in environments where the ingestion feature is exposed to untrusted users.
Exploit
An attacker can exploit this vulnerability by sending a crafted ingestion request to an internet-facing OpenCTI instance. The request would contain a URL pointing to an internal service, such as `http://localhost:9200` (Elasticsearch) or `http://169.254.169.254` (AWS metadata service). The OpenCTI server would then use Axios to make a request to this internal URL, potentially exposing sensitive information or allowing further attacks.
Example of a malicious ingestion request using `curl`:
curl -X POST "https://opencti.example.com/api/ingestion/upload" \
-H "Authorization: Bearer <API_KEY>" \
-H "Content-Type: application/json" \
-d '{"source_url": "http://169.254.169.254/latest/meta-data/iam/security-credentials/"}'
In this example, the `source_url` parameter is set to the AWS metadata service endpoint. If the OpenCTI instance is hosted on AWS, this request could return IAM credentials.
Protection
- Upgrade OpenCTI: The primary and most effective protection is to upgrade OpenCTI to version 6.8.16 or later, which contains the vendor fix for this vulnerability.
- Restrict Access: If an immediate upgrade is not possible, restrict or disable the data ingestion endpoint for untrusted sources.
- Network Segmentation: Implement network segmentation to limit the ability of the OpenCTI instance to reach internal services. Use firewalls to restrict outbound traffic from the OpenCTI server to only necessary external endpoints.
- Input Validation: Implement strict validation and sanitization of all user-supplied URLs. Use an allowlist of permitted domains or protocols.
- Monitor Outbound Requests: Continuously monitor outbound requests from the OpenCTI instance for suspicious or unexpected traffic.
Impact
Successful exploitation of this vulnerability allows an attacker to:
– Internal Network Exposure: Reach internal services that are not publicly exposed, such as Elasticsearch, Redis, or RabbitMQ.
– Sensitive Data Extraction: Extract sensitive data from internal services.
– Cloud Metadata Access: In cloud environments, target metadata services like AWS, Azure, or GCP to obtain credentials and configuration details, potentially leading to full compromise of the infrastructure.
– Enumeration and Data Exfiltration: Enable enumeration of internal systems and data exfiltration.
– Potential Remote Code Execution: In some cases, remote code execution if internal APIs expose dangerous functionality.
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
