CVE-2026-4366
Description
A flaw was identified in Keycloak, an identity and access management solution, where it improperly follows HTTP redirects when processing certain client configuration requests. This behavior allows an attacker to trick the server into making unintended requests to internal or restricted resources. As a result, sensitive internal services such as cloud metadata endpoints could be accessed. This issue may lead to information disclosure and enable attackers to map internal network infrastructure.
Statement
MODERATE impact: Keycloak is vulnerable to a blind Server-Side Request Forgery (SSRF) due to improper handling of HTTP redirects during client configuration. An attacker can exploit this remotely without authentication or user interaction by crafting a sector_identifier_uri that redirects to internal resources, potentially leading to information disclosure and internal network reconnaissance.
Mitigation
To mitigate this vulnerability, restrict the outbound network access of the Keycloak instance. Configure firewall rules to prevent the Keycloak server from initiating connections to internal network segments, especially to well-known cloud metadata service IP addresses such as `169.254.169.254`. For example, on Red Hat Enterprise Linux, you can use `firewalld` to add a rich rule:
`sudo firewall-cmd --permanent --zone=public --add-rich-rule='rule family="ipv4" destination address="169.254.169.254" reject'`
`sudo firewall-cmd --reload`
This may impact other services if they legitimately rely on accessing these internal IPs. Additionally, ensure that any configured `sector_identifier_uri` values are thoroughly validated to only point to trusted, external URLs that do not perform redirects to internal resources.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.8 | N/A | 5.8 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Changed | N/A | Changed |
| Confidentiality | Low | N/A | Low |
| Integrity Impact | None | N/A | None |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data
Integrity
Technical Impact: Execute Unauthorized Code or Commands
Access Control
Technical Impact: Bypass Protection Mechanism
By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls that prevent the attackers from accessing the URLs directly. The server can be used as a proxy to conduct port scanning of hosts in internal networks, use other URLs such as that can access documents on the system (using file://), or use other protocols such as gopher:// or tftp://, which may provide greater control over the contents of requests.
Acknowledgements
Red Hat would like to thank Georgije Vukov (Elite Security Systems) for reporting this issue.
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