CVE-2016-2569 in Squid
Summary
by MITRE
Squid 3.x before 3.5.15 and 4.x before 4.0.7 does not properly append data to String objects, which allows remote servers to cause a denial of service (assertion failure and daemon exit) via a long string, as demonstrated by a crafted HTTP Vary header.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2016-2569 affects Squid proxy server versions 3.x before 3.5.15 and 4.x before 4.0.7, representing a critical flaw in the software's string handling mechanisms that can be exploited to cause remote denial of service conditions. This vulnerability specifically targets the improper appending of data to String objects within the Squid proxy implementation, creating a scenario where malicious remote servers can manipulate the proxy's behavior through crafted HTTP headers. The issue manifests when the proxy receives a particularly long string in the HTTP Vary header, which triggers an assertion failure leading to daemon termination and complete service disruption for all users relying on that proxy server.
The technical root cause of this vulnerability lies in the flawed string manipulation routines within Squid's core codebase, where the software fails to properly handle boundary conditions when appending data to existing String objects. This type of flaw falls under the CWE-129 category of "Improper Validation of Array Index" and is closely related to memory safety issues that can lead to assertion failures and program termination. When a malicious server sends an HTTP Vary header containing an excessively long string, the Squid proxy attempts to append this data to an existing string object without proper bounds checking, resulting in memory corruption that triggers an assertion failure. The vulnerability demonstrates a classic example of how improper string handling can lead to denial of service conditions, as described in the ATT&CK framework under the technique of "Denial of Service" with specific implications for proxy server infrastructure.
The operational impact of CVE-2016-2569 is severe for organizations relying on Squid proxy servers, as it can lead to complete service outages affecting all users who depend on that proxy for internet access or application connectivity. The vulnerability is particularly dangerous because it requires no authentication or privileged access from the attacker, making it a straightforward remote exploit that can be executed from any network location. Network administrators may experience significant disruption as the proxy daemon terminates and restarts, potentially causing temporary loss of internet connectivity for entire departments or organizations. The attack vector is well-defined and easily reproducible, as demonstrated by the specific HTTP Vary header exploitation method, making it a preferred target for malicious actors seeking to disrupt proxy-based network services. Organizations using affected Squid versions face the risk of sustained denial of service conditions that can impact business operations and user productivity.
Mitigation strategies for CVE-2016-2569 primarily involve immediate patching of affected Squid installations to versions 3.5.15 or 4.0.7, which contain the necessary fixes for the string handling routines. System administrators should prioritize updating their Squid proxy servers to prevent exploitation, as the vulnerability provides no legitimate access to system resources beyond service disruption. Additionally, network monitoring should be enhanced to detect unusual HTTP Vary header patterns that might indicate exploitation attempts, though this approach provides only detection rather than prevention. Organizations may also implement temporary workarounds such as disabling specific HTTP header processing or implementing rate limiting for proxy requests, though these measures are less effective than proper patching. The vulnerability underscores the importance of maintaining up-to-date proxy server software and implementing robust security monitoring to detect and respond to exploitation attempts before they can cause significant operational disruption. Regular security assessments of proxy infrastructure should include verification of software versions against known vulnerability databases to prevent similar issues from affecting network infrastructure.