CVE-2018-15178 in Gogs
Summary
by MITRE
Open redirect vulnerability in Gogs before 0.12 allows remote attackers to redirect users to arbitrary websites and conduct phishing attacks via an initial /\ substring in the user/login redirect_to parameter, related to the function isValidRedirect in routes/user/auth.go.
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Analysis
by VulDB Data Team • 05/01/2023
The vulnerability identified as CVE-2018-15178 represents a critical open redirect flaw in the Gogs git repository management system prior to version 0.12. This vulnerability resides in the authentication handling mechanism of the web application, specifically within the routes/user/auth.go file where the isValidRedirect function fails to properly validate redirect URLs. The flaw manifests when an attacker crafts a malicious redirect_to parameter containing an initial forward slash substring, which bypasses the intended security checks and allows arbitrary redirection to external domains.
The technical implementation of this vulnerability stems from insufficient input validation within the authentication redirect logic. When users attempt to log in to a Gogs instance, they are typically redirected to a specified URL after successful authentication. The isValidRedirect function in auth.go is responsible for ensuring that these redirects point to legitimate internal resources rather than external malicious domains. However, the function fails to properly sanitize or validate redirect URLs that begin with a forward slash character, allowing attackers to craft URLs that appear to be internal but actually point to external sites. This weakness enables attackers to manipulate the redirect behavior through carefully crafted malicious URLs that exploit the overly permissive validation logic.
The operational impact of this vulnerability is severe and directly enables sophisticated phishing attacks against users of affected Gogs installations. Attackers can craft deceptive login pages that appear to be legitimate Gogs interfaces while actually redirecting users to malicious external sites designed to harvest credentials or install malware. The vulnerability is particularly dangerous because it leverages the trust relationship between users and the Gogs application, making it more likely that victims will fall for social engineering tactics. This opens the door to credential theft, session hijacking, and other forms of account compromise that can escalate to full system compromise if attackers gain access to privileged accounts.
Organizations using affected versions of Gogs should immediately apply the security patch released with version 0.12 to address this vulnerability. The fix involves strengthening the isValidRedirect function to properly validate all redirect URLs regardless of their initial character sequence, ensuring that only legitimate internal paths are accepted for redirection. Additionally, administrators should implement network-level controls to monitor and restrict outbound traffic from their Gogs instances, particularly to suspicious domains. This vulnerability aligns with CWE-601, which addresses open redirect vulnerabilities, and maps to ATT&CK technique T1566.001 for credential harvesting through phishing attacks. Security teams should also conduct comprehensive audits of their authentication systems to identify similar validation flaws that may exist in other components of their infrastructure.
The remediation process requires careful testing to ensure that legitimate internal redirects continue to function properly while eliminating the security gap that allows external redirection. Organizations should also consider implementing additional security measures such as domain-based message authentication, reporting, and conformance (DMARC) policies to protect against phishing attacks that may exploit this vulnerability. Regular security assessments of web applications should include thorough validation of all redirect mechanisms to prevent similar issues from emerging in other systems. The vulnerability demonstrates the critical importance of proper input validation in authentication flows and highlights the need for robust security testing practices that examine edge cases in URL handling and redirection logic.