CVE-2015-2296 in Requests
Summary
by MITRE
The resolve_redirects function in sessions.py in requests 2.1.0 through 2.5.3 allows remote attackers to conduct session fixation attacks via a cookie without a host value in a redirect.
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Analysis
by VulDB Data Team • 03/19/2026
The vulnerability identified as CVE-2015-2296 resides within the requests library version 2.1.0 through 2.5.3, specifically in the resolve_redirects function located in sessions.py. This flaw represents a significant security weakness that enables remote attackers to execute session fixation attacks by manipulating cookie values during HTTP redirect operations. The vulnerability stems from the library's improper handling of cookies that lack host values, creating an exploitable condition where attacker-controlled redirects can manipulate session identifiers. The requests library serves as a fundamental HTTP client component widely used across numerous applications and frameworks, making this vulnerability particularly dangerous as it affects a substantial portion of the software ecosystem that relies on HTTP communication.
The technical implementation of this vulnerability occurs when the resolve_redirects function processes HTTP redirects and encounters cookies without explicit host values. During redirect handling, the library fails to properly validate or sanitize cookie attributes, allowing malicious actors to inject session cookies that can persist across redirect boundaries. This flaw directly violates security principles related to session management and cookie handling, as it enables attackers to establish session identifiers that remain consistent across different host contexts. The vulnerability operates at the HTTP protocol level within the session management subsystem, where the library's redirect resolution logic does not adequately separate or validate cookie contexts, creating opportunities for session hijacking and fixation attacks. According to CWE classification, this represents a weakness in session management and cookie handling practices, specifically CWE-384 which addresses session fixation vulnerabilities.
The operational impact of CVE-2015-2296 extends far beyond individual application instances due to the widespread adoption of the requests library across various programming languages and frameworks. Applications leveraging this library for HTTP communication become vulnerable to session fixation attacks where attackers can manipulate user sessions by controlling redirect responses and cookie values. This vulnerability enables unauthorized access to user accounts, session takeover scenarios, and potential data breaches when applications depend on the requests library for authentication flows. The attack vector is particularly concerning because it requires minimal privileges to exploit and can be automated through various redirection techniques. Security professionals should consider this vulnerability in relation to ATT&CK framework techniques such as T1566 for credential access through social engineering and T1075 for remote access using legitimate credentials, as session fixation attacks often lead to broader compromise scenarios.
Mitigation strategies for CVE-2015-2296 primarily involve upgrading to requests library versions 2.6.0 or later, where the vulnerability has been addressed through improved cookie handling and redirect validation mechanisms. Organizations should conduct comprehensive vulnerability assessments to identify all systems utilizing affected library versions and prioritize remediation efforts accordingly. Additional defensive measures include implementing proper cookie security attributes such as HttpOnly, Secure, and SameSite flags, along with monitoring redirect patterns for suspicious cookie modifications. Network-level controls such as web application firewalls can help detect and block malicious redirect attempts, while application-level defenses should include session regeneration upon authentication and proper validation of redirect destinations. The fix implemented in newer versions addresses the core issue by ensuring that cookie host values are properly validated during redirect processing, preventing the persistence of attacker-controlled session identifiers across different host contexts. Organizations should also consider implementing automated dependency scanning tools to identify and remediate similar vulnerabilities in their software supply chains, as this vulnerability demonstrates the critical importance of maintaining up-to-date third-party libraries in security-conscious environments.