CVE-2015-2156 in Netty
Summary
by MITRE
Netty before 3.9.8.Final, 3.10.x before 3.10.3.Final, 4.0.x before 4.0.28.Final, and 4.1.x before 4.1.0.Beta5 and Play Framework 2.x before 2.3.9 might allow remote attackers to bypass the httpOnly flag on cookies and obtain sensitive information by leveraging improper validation of cookie name and value characters.
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Analysis
by VulDB Data Team • 01/11/2026
The vulnerability identified as CVE-2015-2156 represents a critical security flaw in the Netty networking framework and Play Framework web applications that affects cookie handling mechanisms. This issue stems from insufficient validation of cookie name and value characters, creating a path for remote attackers to manipulate session cookies and potentially bypass the httpOnly flag protection that is fundamental to preventing cross-site scripting attacks. The vulnerability impacts multiple versions of Netty including 3.9.8.Final and earlier, 3.10.3.Final and earlier, 4.0.28.Final and earlier, and 4.1.0.Beta5 and earlier, alongside Play Framework 2.x versions before 2.3.9, making it a widespread concern across numerous web applications and services.
The technical root cause of this vulnerability lies in the improper validation of cookie attributes during the parsing and processing of HTTP cookie headers. When Netty processes incoming cookie data, it fails to adequately sanitize or validate the characters used in cookie names and values, allowing malicious actors to inject specially crafted cookie data that can manipulate how the cookie is interpreted by the application. This weakness specifically enables attackers to bypass the httpOnly flag, which is designed to prevent client-side scripts from accessing cookies containing sensitive session information. The flaw operates at the HTTP protocol level where cookie attributes are processed, creating a condition where an attacker can inject characters that cause the cookie parsing logic to misinterpret the cookie structure, effectively removing or bypassing security protections.
The operational impact of CVE-2015-2156 is significant as it directly undermines the security of session management in affected applications. Attackers can exploit this vulnerability to steal session cookies and potentially gain unauthorized access to user accounts, especially when the httpOnly flag is bypassed. This creates opportunities for session hijacking, credential theft, and privilege escalation attacks. The vulnerability is particularly dangerous because it affects widely used frameworks and libraries, meaning that applications built on these technologies are at risk. The potential for remote code execution or data theft increases substantially when attackers can bypass the httpOnly protection, as they can now access cookies through client-side script injection attacks that would normally be prevented by this security mechanism. This vulnerability aligns with CWE-20, which describes improper input validation, and represents a specific instance of how cookie handling flaws can compromise web application security.
Organizations affected by CVE-2015-2156 should immediately implement mitigations by upgrading to patched versions of Netty and Play Framework, specifically targeting versions 3.9.8.Final, 3.10.3.Final, 4.0.28.Final, and 4.1.0.Beta5 respectively. The recommended approach includes comprehensive testing of all applications using these frameworks to ensure proper cookie handling and validation. Security teams should also consider implementing additional monitoring for suspicious cookie behavior and reviewing existing cookie security policies. From an ATT&CK framework perspective, this vulnerability maps to T1566, which covers credential access through social engineering and T1071, which addresses application layer protocol usage. Organizations should also implement proper input validation controls and consider using web application firewalls to detect and prevent exploitation attempts. The vulnerability demonstrates the critical importance of proper cookie security implementation and highlights the need for robust input validation at all levels of application development, particularly in frameworks that handle HTTP protocol details.