CVE-2026-4981
Description
A flaw was found in Red Hat Advanced Cluster Security (ACS). An unauthenticated remote attacker can exploit a vulnerability in the login interface's OAuth callback endpoint by crafting a malicious URL. This URL, containing unvalidated error and error_uri parameters, allows the attacker to display arbitrary error messages, leading to content spoofing. Furthermore, the attacker can redirect victims to malicious domains, effectively performing an open redirect under the guise of the trusted application's user interface.
Statement
This Moderate impact vulnerability in Red Hat Advanced Cluster Security (ACS) allows an unauthenticated remote attacker to perform open redirect and content spoofing. By crafting a malicious URL with unvalidated parameters in the OAuth callback endpoint, an attacker can display arbitrary error messages and redirect users to malicious domains, appearing as the trusted application UI. This primarily affects user interaction with the login interface.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.4 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | Required | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | Low | N/A | N/A |
| Integrity Impact | Low | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity
The user may be redirected to an untrusted page that contains malware which may then compromise the user's system. In some cases, an open redirect can also enable the immediate download of a file without the user's permission, because the redirection to an external site may lead to endpoints on those sites that automatically trigger a download action ("drive-by download" [REF-1478]). This will expose the user to extensive risk. The user's interaction with the web server may also be compromised if the malware conducts keylogging or other attacks that steal credentials, personally identifiable information (PII), or other important data.
Access Control,Confidentiality,Other
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity; Other
By modifying the URL value to a malicious site, an attacker may successfully launch a phishing scam. The user may be subjected to phishing attacks by being redirected to an untrusted page. The phishing attack may point to an attacker controlled web page that appears to be a trusted web site. The phishers may then steal the user's credentials and then use these credentials to access the legitimate web site. Because the server name in the modified link is identical to the original site, phishing attempts have a more trustworthy appearance.
Acknowledgements
This issue was discovered by Àngel Ollé Blázquez (Red Hat).
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