How severe is CVE-2026-21887?

CVE-2026-21887 has a CVSS 3.x base score of 7.7, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2026-21887 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21887?

CVE-2026-21887 affects Citeum Opencti. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-21887?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-21887 have an EU (EUVD) identifier?

Yes. CVE-2026-21887 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-11599.

When was CVE-2026-21887 published?

CVE-2026-21887 was published on 2026-03-12 and last updated on 2026-06-17.

CVE-2026-21887

CVE-2026-21887 is a high-severity vulnerability in Citeum Opencti with a CVSS 3.x base score of 7.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-918.

Key facts

Severity: High (CVSS 3.x base score 7.7)
EPSS exploit prediction: 0% (11th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-11599
Weakness: CWE-918
Affected product: Citeum Opencti
Published: 2026-03-12
Last modified: 2026-06-17

Description

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). 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.

Frequently asked questions

What is CVE-2026-21887?: 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). 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.
How severe is CVE-2026-21887?: CVE-2026-21887 has a CVSS 3.x base score of 7.7, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2026-21887 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21887?: CVE-2026-21887 affects Citeum Opencti. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-21887?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-21887 have an EU (EUVD) identifier?: Yes. CVE-2026-21887 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-11599.
When was CVE-2026-21887 published?: CVE-2026-21887 was published on 2026-03-12 and last updated on 2026-06-17.

References

https://github.com/OpenCTI-Platform/opencti/security/advisories/GHSA-ffm6-vvph-g5f5

EU advisories (EUVD)

Affected products (1)

cpe:2.3:a:citeum:opencti:*:*:*:*:*:*:*:*

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