CVE-2023-30861 is a high-severity vulnerability affecting Flask, a lightweight WSGI web application framework. The vulnerability arises when a response containing data intended for a specific client is cached and subsequently sent by a proxy to other clients, potentially exposing one client's session cookie to others. This vulnerability requires a specific set of conditions to be exploited, making the risk contextually dependent on the application's deployment.
The CVSS score for this vulnerability is 7.5, indicating a high severity level. Organizations utilizing Flask should be particularly concerned about this issue, as it may lead to unauthorized access to sensitive session data. The urgency for organizations is heightened due to the potential impact on confidentiality, as attackers may leverage cached session information.
To protect against this vulnerability, organizations should prioritize patching immediately. The vulnerability has been addressed in Flask versions 2.3.2 and 2.2.5. It is essential for organizations to ensure that they are running the latest version of Flask to mitigate the associated risks.
If your application meets the following criteria, it may be vulnerable: hosted behind a caching proxy that does not strip cookies, sets `session.permanent = True`, does not modify the session during a request, has `SESSION_REFRESH_EACH_REQUEST` enabled, and does not set a `Cache-Control` header to prevent caching.
Given the implications of this vulnerability, organizations should act decisively to patch affected systems and review their caching configurations.
Vulnerability Details
CVE-2023-30861 is classified under CWE-539, which pertains to the improper exposure of sensitive information. The vulnerability allows a caching proxy to send one client's `session` cookie to other clients under specific conditions. This issue is exacerbated when the application does not employ proper cache controls.
Flask versions prior to 2.3.2 and 2.2.5 are affected. The vulnerability's publication date was May 2, 2023, and it has been modified as new information has become available.
Technical Analysis
The root cause of this vulnerability lies in Flask's handling of session cookies and caching. When the session is not accessed or modified during a request, the framework does not set the `Vary: Cookie` header appropriately, allowing the proxy to cache responses that include sensitive session data.
The attack vector is network-based, with a low attack complexity. No privileges are required to exploit this vulnerability, and user interaction is not necessary. The confidentiality impact is categorized as high, while the integrity and availability impacts are none.
Risk & Impact Analysis
Risk to organizations includes potential unauthorized access to sensitive session data, which could lead to further attacks or data breaches. The blast radius of this vulnerability can be significant if exploited, particularly in environments where multiple users share access to the same application instance. Given the high CVSS score and the public availability of exploit information, organizations must assess their exposure to this risk.
The urgency for remediation is high, especially for applications that rely on Flask for session management. Organizations should evaluate their current use of caching proxies and implement necessary changes to minimize exposure.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | Yes |
Public PoC | Yes |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
Flask versions 2.3.0 to 2.3.1 and all versions prior to 2.2.5 are affected by this vulnerability. Organizations should ensure they upgrade to at least version 2.3.2 or 2.2.5.
Mitigation & Remediation
Organizations should prioritize patching by upgrading to the latest version of Flask. If immediate patching is not possible, consider implementing configuration hardening by setting appropriate `Cache-Control` headers to prevent caching of sensitive data. Additionally, review the deployment of caching proxies to ensure they do not expose session cookies.
For further guidance on securing web applications, organizations can refer to our application security assessment services that provide expert insight into mitigating vulnerabilities.
Detection Guidance
To detect potential exploitation of this vulnerability, monitor logs for unusual access patterns that might indicate unauthorized session access. Behavioral anomalies in user sessions, such as unexpected logins from different IP addresses, should be investigated. Implementing network signatures that can detect abnormal caching behavior may also aid in identifying attempts to exploit this vulnerability.
AppSecure Threat Intelligence Insight
CVE-2023-30861 serves as a reminder of the complexities involved in web application security, particularly regarding session management and caching mechanisms. The low EPSS score indicates a relatively low probability of exploitation in the wild, but the high severity underscores the need for vigilance in application deployments.
Organizations should learn from this incident and ensure robust security practices in their development and deployment processes. Regular security audits and adherence to best practices in application security can significantly reduce the risk of similar vulnerabilities in the future.
For additional insights into web application security vulnerabilities and their management, refer to our penetration testing methodology blog, which provides comprehensive guidance.
Additionally, following a vulnerability management program can help organizations identify and remediate vulnerabilities proactively.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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