CVE-2026-40181
Description
A flaw was found in React Router. This vulnerability allows a remote attacker to redirect users to an external, potentially malicious, website. This occurs when specially crafted URLs, containing paths starting with //, are passed to the redirect function, causing them to be misinterpreted as protocol-relative URLs. The severity of the impact depends on how the application validates redirects.
Statement
A Moderate impact open redirect vulnerability exists in React Router, affecting versions 7.0.0 through 7.14.0 and 6.7.0 through 6.30.3. This flaw allows a remote attacker to redirect users to arbitrary external websites by crafting URLs that begin with //, which are then misinterpreted as protocol-relative. The exploitability and actual impact on Red Hat products depend on the specific application's redirect validation logic. Applications utilizing React Router in Declarative Mode (<BrowserRouter>) are not affected by this issue.
Mitigation
Application developers using React Router in Red Hat products should implement robust URL validation before performing redirects to prevent misinterpretation of protocol-relative URLs. Additionally, applications configured with Declarative Mode (<BrowserRouter>) are not impacted by this vulnerability. Users should exercise caution when interacting with untrusted links.
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 | 5.4 | 6.1 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | Required | Required | N/A |
| Scope | Unchanged | Changed | N/A |
| Confidentiality | Low | Low | N/A |
| Integrity Impact | Low | Low | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/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.
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