Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:NSummary
CVE-2026-21887 is a high-severity SSRF (CWE-918) vulnerability in Citeum Opencti. Its CVSS base score is 7.7 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 12th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-21887 is a server-side request forgery (SSRF) vulnerability, classified under CWE-918, affecting the OpenCTI open-source platform for managing cyber threat intelligence knowledge and observables. In versions prior to 6.8.16, the data ingestion feature accepts user-supplied URLs without validation and relies on the Axios HTTP client configured with its default allowAbsoluteUrls: true setting. This enables attackers to direct requests to arbitrary endpoints, including internal services, as Axios processes absolute URLs without restriction, resulting in a semi-blind SSRF where responses may not be fully visible to the attacker.
The vulnerability has a CVSS v3.1 base score of 7.7 (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N), indicating exploitation over the network with low complexity, requiring only low privileges, no user interaction, and a changed scope with high confidentiality impact. Authenticated users with low privileges can craft malicious URLs during data ingestion to trigger requests to internal systems, potentially allowing unauthorized access to sensitive data on those systems, though the impact is limited to information disclosure without integrity or availability effects.
The vulnerability is addressed in OpenCTI version 6.8.16, as detailed in the GitHub security advisory at https://github.com/OpenCTI-Platform/opencti/security/advisories/GHSA-ffm6-vvph-g5f5. Security practitioners should upgrade to the patched version to mitigate the SSRF risk.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-11599
Vulnerability Data
OpenCTI is an open source platform for managing cyber threat intelligence knowledge and observables. Prior to 6.8.16, the OpenCTI platform’s data ingestion feature accepts user-supplied URLs without validation and uses the Axios HTTP client with its default configuration (allowAbsoluteUrls: true).…
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This allows attackers to craft requests to arbitrary endpoints, including internal services, because Axios will accept and process absolute URLs. This results in a semi-blind SSRF, as responses may not be fully visible but can still impact internal systems. This vulnerability is fixed in 6.8.16.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.3.6V1.5.3V5.3.2V10.4.7
Mitigating Controls (NIST 800-53 r5) AI
Information flow enforcement can restrict which destinations the server is allowed to contact on behalf of users.
Input validation directly stops untrusted URLs from being accepted and fetched without destination checks.
Boundary protection limits the network reach of server-initiated requests even if SSRF occurs.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure development practices directly include input validation and destination allow-listing that prevent SSRF.
Runtime monitoring of web applications and services can detect anomalous outbound requests indicative of SSRF.
Vulnerability identification processes can discover and record SSRF flaws in web applications.
Network segmentation and egress controls can limit the damage from successful SSRF requests.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Operational threat data describing SSRF campaigns can be used to tighten outbound-request allow-lists and detection rules before attackers exploit them.