CVE-2015-8852 in Varnish
Summary
by MITRE
Varnish 3.x before 3.0.7, when used in certain stacked installations, allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via a header line terminated by a \r (carriage return) character in conjunction with multiple Content-Length headers in an HTTP request.
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Analysis
by VulDB Data Team • 11/07/2024
The vulnerability identified as CVE-2015-8852 represents a critical security flaw in Varnish Cache versions 3.x prior to 3.0.7 that manifests specifically in stacked deployment configurations. This issue stems from inadequate input validation and header processing mechanisms within the caching proxy server, creating a pathway for remote attackers to manipulate HTTP responses through carefully crafted malicious requests. The vulnerability is particularly concerning because it enables attackers to inject arbitrary HTTP headers into responses, potentially leading to serious security implications including session hijacking, cross-site scripting attacks, and other forms of web application compromise.
The technical exploitation of this vulnerability relies on the manipulation of HTTP request headers through a specific combination of elements that exploit parsing inconsistencies in Varnish's header handling. Attackers can construct requests containing header lines terminated by carriage return characters followed by multiple Content-Length headers, which creates a condition where the caching server fails to properly validate and sanitize header inputs. This parsing failure occurs in stacked installations where multiple Varnish instances or components interact, amplifying the attack surface and making the vulnerability more accessible. The flaw essentially allows attackers to bypass normal security controls by injecting malicious headers that get processed and forwarded in subsequent HTTP responses.
The operational impact of CVE-2015-8852 extends beyond simple header injection, as it enables HTTP response splitting attacks that can be leveraged for sophisticated web application attacks. When successful, these attacks can manipulate how web browsers process responses, potentially allowing attackers to inject malicious content into web pages or redirect users to malicious sites. The vulnerability affects organizations using Varnish Cache in production environments where stacked configurations are common, particularly in high-traffic scenarios where caching performance is critical. This makes the vulnerability particularly dangerous for web applications that rely heavily on caching mechanisms for performance optimization.
Organizations affected by this vulnerability should prioritize immediate patching of Varnish Cache installations to version 3.0.7 or later, which contains the necessary fixes for header validation and processing. Additionally, implementing network-level mitigations such as web application firewalls can provide additional protection against exploitation attempts. Security teams should also conduct thorough assessments of their stacked Varnish configurations to identify potential exposure points and ensure proper input validation is in place. The vulnerability aligns with CWE-1127, which addresses improper handling of HTTP headers, and maps to ATT&CK technique T1190 for exploiting vulnerabilities in web applications, making it a significant concern for organizations following standard security frameworks and threat modeling practices.