How severe is CVE-2026-54221?

CVE-2026-54221 has a CVSS 4.0 base score of 5.1, rated medium severity.

Is CVE-2026-54221 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-54221?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-54221 have an EU (EUVD) identifier?

Yes. CVE-2026-54221 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37884.

When was CVE-2026-54221 published?

CVE-2026-54221 was published on 2026-06-18.

CVE-2026-54221

CVE-2026-54221 is a medium-severity vulnerability with a CVSS 4.0 base score of 5.1. 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-79.

Key facts

Severity: Medium (CVSS 4.0 base score 5.1)
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-37884
Weakness: CWE-79
Published: 2026-06-18
Last modified: 2026-06-18

Description

UBB.threads is vulnerable to Reflected XSS. The application improperly handles user input in certain requests, enabling attackers to execute arbitrary JavaScript in the context of a victim's browser by tricking them into clicking a crafted link. Because vendor contact attempts were unsuccessful, the vulnerability has only been confirmed in version 7.7.5 but may also affect other versions.

Frequently asked questions

What is CVE-2026-54221?: UBB.threads is vulnerable to Reflected XSS. The application improperly handles user input in certain requests, enabling attackers to execute arbitrary JavaScript in the context of a victim's browser by tricking them into clicking a crafted link. Because vendor contact attempts were unsuccessful, the vulnerability has only been confirmed in version 7.7.5 but may also affect other versions.
How severe is CVE-2026-54221?: CVE-2026-54221 has a CVSS 4.0 base score of 5.1, rated medium severity.
Is CVE-2026-54221 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-54221?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-54221 have an EU (EUVD) identifier?: Yes. CVE-2026-54221 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37884.
When was CVE-2026-54221 published?: CVE-2026-54221 was published on 2026-06-18.

References

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