How severe is CVE-2021-3637?

CVE-2021-3637 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-3637 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (62nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3637?

CVE-2021-3637 primarily affects Redhat Keycloak. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-3637?

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.

When was CVE-2021-3637 published?

CVE-2021-3637 was published on 2021-07-09 and last updated on 2026-06-17.

CVE-2021-3637

CVE-2021-3637 is a high-severity vulnerability in Redhat Keycloak with a CVSS 3.x base score of 7.5. 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-770.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (62nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-770
Affected product: Redhat Keycloak
Published: 2021-07-09
Last modified: 2026-06-17

Description

A flaw was found in keycloak-model-infinispan in keycloak versions before 14.0.0 where authenticationSessions map in RootAuthenticationSessionEntity grows boundlessly which could lead to a DoS attack.

Frequently asked questions

What is CVE-2021-3637?: A flaw was found in keycloak-model-infinispan in keycloak versions before 14.0.0 where authenticationSessions map in RootAuthenticationSessionEntity grows boundlessly which could lead to a DoS attack.
How severe is CVE-2021-3637?: CVE-2021-3637 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-3637 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (62nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3637?: CVE-2021-3637 primarily affects Redhat Keycloak. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-3637?: 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.
When was CVE-2021-3637 published?: CVE-2021-3637 was published on 2021-07-09 and last updated on 2026-06-17.

References

https://bugzilla.redhat.com/show_bug.cgi?id=1979638

Affected products (2)

cpe:2.3:a:redhat:keycloak:*:*:*:*:*:*:*:*
cpe:2.3:a:redhat:single_sign-on:7.0:*:*:*:*:*:*:*

More vulnerabilities in Redhat Keycloak

CVE-2022-4361 — Critical (CVSS 10.0): Keycloak, an open-source identity and access management solution, has a cross-site scripting (XSS) vulnerability in the…
CVE-2022-1245 — Critical (CVSS 9.8): A privilege escalation flaw was found in the token exchange feature of keycloak. Missing authorization allows a client…
CVE-2019-14910 — Critical (CVSS 9.8): A vulnerability was found in keycloak 7.x, when keycloak is configured with LDAP user federation and StartTLS is used…
CVE-2021-20195 — Critical (CVSS 9.6): A flaw was found in keycloak in versions before 13.0.0. A Self Stored XSS attack vector escalating to a complete…
CVE-2022-3782 — Critical (CVSS 9.1): keycloak: path traversal via double URL encoding. A flaw was found in Keycloak, where it does not properly validate…
CVE-2019-14837 — Critical (CVSS 9.1): A flaw was found in keycloack before version 8.0.0. The owner of 'placeholder.org' domain can setup mail server on this…

All CVEs affecting Redhat Keycloak →

Other CWE-770 (Allocation of Resources Without Limits or Throttling) vulnerabilities

CVE-2026-31283 — Critical (CVSS 9.8): In Totara LMS v19.1.5 and before, the forgot password API does not implement rate limiting for the target email…
CVE-2020-37067 — Critical (CVSS 9.8): Filetto 1.0 FTP server contains a denial of service vulnerability in the FEAT command processing that allows attackers…
CVE-2021-47875 — Critical (CVSS 9.8): GeoGebra CAS Calculator 6.0.631.0 contains a denial of service vulnerability that allows attackers to crash the…
CVE-2025-11832 — Critical (CVSS 9.8): Allocation of Resources Without Limits or Throttling vulnerability in Azure Access Technology BLU-IC2, Azure Access…
CVE-2024-44241 — Critical (CVSS 9.8): The issue was addressed with improved bounds checks. This issue is fixed in iOS 18.1 and iPadOS 18.1, macOS Sequoia…
CVE-2022-3439 — Critical (CVSS 9.8): Allocation of Resources Without Limits or Throttling in GitHub repository ikus060/rdiffweb prior to 2.5.0.

Browse all CWE-770 (Allocation of Resources Without Limits or Throttling) vulnerabilities →