CVE-2025-29927 is a critical vulnerability in Vercel's Next.js, a popular React framework for building full-stack web applications. This vulnerability allows attackers to bypass authorization checks if those checks occur within middleware, impacting the confidentiality and integrity of the application. The potential risk is significant, as unauthorized access could lead to sensitive data exposure and manipulation.
The severity of this vulnerability is rated as critical, with a CVSS score of 9.1. This high score indicates that the vulnerability can be exploited with relatively low complexity and no user interaction is required. Given the critical nature of the vulnerability and its potential impact on organizations using Next.js, it is imperative to address it promptly.
Organizations should prioritize patching immediately, particularly those running versions 1.11.4 through 12.3.5, 13.5.9, 14.2.25, and 15.2.3 of Next.js, which are affected. If immediate patching is not feasible, it is advised to restrict external user requests containing the x-middleware-subrequest header from reaching the Next.js application.
As of the latest analysis, exploits for this vulnerability are known to exist, highlighting the urgency for organizations to remediate this issue.
Vulnerability Details
The vulnerability description indicates that starting from version 1.11.4 and prior to versions 12.3.5, 13.5.9, 14.2.25, and 15.2.3, it is possible to bypass authorization checks if those checks are conducted in middleware. The official CVE description emphasizes the risk posed by this flaw and provides guidance for mitigation.
The CVSS score of 9.1 indicates a critical severity level. This score reflects the vulnerability's potential for exploitation, particularly in networked environments where the attack vector is classified as 'NETWORK'. The confidentiality and integrity impacts are rated as high, while availability is noted as none.
Affected products include Next.js, with the vendor being Vercel. The vulnerability was published on March 21, 2025, and it falls under CWE-285 (Improper Authorization) and CWE-863 (Authorization Bypass Through User-Controlled Key).
Technical Analysis
The root cause of CVE-2025-29927 lies in the implementation of middleware authorization checks within Next.js applications. The vulnerability arises when these checks are bypassed, allowing unauthorized access to functionality and data that would typically require proper authorization.
The attack vector is identified as a network, with low attack complexity. Attackers do not require any privileges or user interaction to exploit this vulnerability, making it especially dangerous. The impact on confidentiality and integrity is categorized as high, while availability is unaffected.
Risk & Impact Analysis
Risk to organizations includes significant exposure of sensitive data and potential manipulation of application functionality. The blast radius of this vulnerability is extensive, as it can affect any Next.js application that utilizes middleware for authorization checks. Organizations that fail to act promptly could face severe security incidents, including data breaches.
Given the critical severity of this vulnerability and its exploitation status, organizations should prioritize patching immediately. The existence of public exploits further complicates the threat landscape, emphasizing the need for swift action.
Signal | Status |
|---|---|
Known Exploit | Yes |
Public PoC | Yes |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The affected versions of Next.js are versions 1.11.4 up to but not including 12.3.5, 13.5.9, 14.2.25, and 15.2.3. Organizations running these versions should apply the necessary patches to mitigate the vulnerability.
Mitigation & Remediation
Organizations should update to the patched versions of Next.js: 12.3.5, 13.5.9, 14.2.25, or 15.2.3 to eliminate this vulnerability. If immediate patching is not feasible, it is recommended to prevent external user requests that contain the x-middleware-subrequest header from reaching your Next.js application.
For further assistance, organizations can consider utilizing penetration testing services to validate the effectiveness of their remediation efforts.
Detection Guidance
Organizations should monitor logs for indicators of unauthorized access attempts and behavioral anomalies that may indicate exploitation of this vulnerability. Network signatures associated with the x-middleware-subrequest header should be tracked, and any changes to system configurations should be logged for review.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-29927 highlights the critical importance of robust authorization checks in application frameworks. This vulnerability serves as a reminder for security teams to continuously evaluate their middleware implementations and ensure that authorization mechanisms are effective.
Organizations can benefit from reviewing their vulnerability management programs to adapt to threats like this. Additionally, leveraging penetration testing methodologies can enhance their ability to detect and respond to similar vulnerabilities in the future.
Finally, it is essential to stay informed about red teaming services as part of a comprehensive security strategy that tests the resilience of applications against real-world attack scenarios.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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