CVE-2017-5474 in Serendipity
Summary
by MITRE
Open redirect vulnerability in comment.php in Serendipity through 2.0.5 allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a URL in the HTTP Referer header.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2017-5474 represents a critical open redirect flaw discovered in the Serendipity blogging platform version 2.0.5 and earlier. This security weakness resides within the comment.php script which fails to properly validate or sanitize URL parameters derived from the HTTP Referer header. The flaw enables malicious actors to manipulate user navigation by redirecting them to arbitrary web addresses without proper validation, creating significant risks for both end users and system administrators. The vulnerability specifically affects the platform's handling of referer information during comment submission processes, where the application does not adequately filter or escape user-supplied URLs that may be present in the HTTP Referer header.
The technical implementation of this vulnerability stems from insufficient input validation within the comment processing logic of Serendipity's comment.php file. When users submit comments to a blog, the system typically captures the HTTP Referer header to determine the page from which the comment originated. However, the application does not perform proper sanitization of this header data before using it in redirect operations. This allows attackers to craft malicious referer values containing crafted URLs that will be interpreted as legitimate redirect targets by the vulnerable application. The flaw operates under CWE-601 which categorizes open redirect vulnerabilities as weaknesses where applications redirect users to external sites without proper validation, potentially leading to phishing attacks and user deception. The vulnerability can be exploited through simple HTTP requests that include malicious referer headers containing URLs pointing to attacker-controlled domains.
The operational impact of this vulnerability extends beyond simple redirection capabilities and creates substantial risk for users and organizations utilizing affected Serendipity installations. Attackers can leverage this weakness to conduct sophisticated phishing campaigns by redirecting users to malicious domains that mimic legitimate websites, potentially harvesting credentials or personal information. The vulnerability allows for the creation of convincing phishing attacks since the redirect originates from what appears to be a legitimate blog domain, making it difficult for users to distinguish between authentic and malicious navigation. This open redirect mechanism provides attackers with a vector for social engineering attacks where users are unknowingly directed to fraudulent websites that may be designed to steal sensitive information or deploy malware. The threat landscape is further complicated by the fact that such vulnerabilities can be combined with other attack vectors to create more sophisticated multi-stage attacks against users and organizations.
Mitigation strategies for CVE-2017-5474 should prioritize immediate patching of affected Serendipity installations to version 2.0.6 or later, which includes proper input validation and sanitization of referer headers. Organizations should implement comprehensive input validation measures that explicitly check and sanitize all URL parameters extracted from HTTP headers, particularly those used in redirect operations. The implementation of a whitelist approach for redirect destinations, where only known and trusted domains are permitted for redirection, provides an additional layer of protection against open redirect attacks. Security teams should also consider implementing network-level controls such as web application firewalls that can detect and block suspicious referer header patterns. According to ATT&CK framework category T1566, which covers phishing techniques, this vulnerability directly enables the execution of phishing attacks through the manipulation of user navigation. System administrators should also conduct thorough security audits of all web applications to identify similar input validation weaknesses and ensure proper security configurations that prevent unauthorized redirection. The remediation process should include comprehensive testing to verify that all redirect operations properly validate input and that the application no longer accepts malicious referer values that could be used to redirect users to unauthorized domains.