How severe is CVE-2021-3856?

CVE-2021-3856 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2021-3856 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3856?

CVE-2021-3856 affects Redhat Keycloak. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-3856?

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

When was CVE-2021-3856 published?

CVE-2021-3856 was published on 2022-08-26 and last updated on 2026-06-17.

CVE-2021-3856

CVE-2021-3856 is a medium-severity vulnerability in Redhat Keycloak with a CVSS 3.x base score of 4.3. 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-22.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
EPSS exploit prediction: 1% (55th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-22
Affected product: Redhat Keycloak
Published: 2022-08-26
Last modified: 2026-06-17

Description

ClassLoaderTheme and ClasspathThemeResourceProviderFactory allows reading any file available as a resource to the classloader. By sending requests for theme resources with a relative path from an external HTTP client, the client will receive the content of random files if available.

Frequently asked questions

What is CVE-2021-3856?: ClassLoaderTheme and ClasspathThemeResourceProviderFactory allows reading any file available as a resource to the classloader. By sending requests for theme resources with a relative path from an external HTTP client, the client will receive the content of random files if available.
How severe is CVE-2021-3856?: CVE-2021-3856 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2021-3856 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3856?: CVE-2021-3856 affects Redhat Keycloak. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-3856?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-3856 published?: CVE-2021-3856 was published on 2022-08-26 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:redhat:keycloak:*:*:*:*:*:*:*:*

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