CVE-2026-27779 in Gitea
Summary
by MITRE • 07/04/2026
Gitea versions before 1.25.5 accept malformed or injected forwarded-proto values when detecting public URLs, allowing spoofed canonical URL generation.
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Analysis
by VulDB Data Team • 07/04/2026
This vulnerability in Gitea versions prior to 1.25.5 represents a critical security flaw that enables attackers to manipulate the application's detection of public URLs through maliciously crafted forwarded-proto headers. The issue stems from inadequate input validation and sanitization mechanisms within the URL canonicalization process, specifically when the application relies on HTTP headers such as X-Forwarded-Proto to determine whether connections are secure or not. When these headers contain malformed or injected values, the system fails to properly validate the input before using it to construct canonical URLs, creating opportunities for attackers to inject arbitrary protocol identifiers and potentially redirect users to malicious endpoints.
The technical implementation of this vulnerability involves the application's reliance on HTTP header information without proper sanitization checks during URL generation processes. When Gitea encounters requests with manipulated X-Forwarded-Proto values, it accepts these inputs directly in its URL construction logic, allowing attackers to craft URLs that appear legitimate but actually point to attacker-controlled domains or endpoints. This type of vulnerability aligns with CWE-20, which covers improper input validation, and specifically relates to insecure handling of HTTP headers. The flaw can be exploited through various attack vectors including man-in-the-middle scenarios, server misconfigurations, or direct injection attacks where an attacker controls network traffic between clients and the application.
The operational impact of this vulnerability is significant as it allows for potential redirection attacks that could lead to phishing, credential theft, or further exploitation within the application ecosystem. An attacker who successfully manipulates the canonical URL generation process can redirect users to malicious sites while maintaining the appearance of legitimate Gitea operations. This creates opportunities for social engineering attacks where users might be tricked into believing they are interacting with authentic Gitea services. The vulnerability also poses risks to internal network security as it could enable attackers to bypass authentication mechanisms or manipulate application behavior through URL-based attacks.
Mitigation strategies for this vulnerability should focus on implementing robust input validation and sanitization of all HTTP headers used in URL construction processes. Organizations should upgrade to Gitea version 1.25.5 or later where the vulnerability has been addressed through proper header validation mechanisms. Additionally, system administrators should implement strict header validation policies that reject malformed or unexpected values in forwarded-proto headers, particularly in environments where multiple layers of proxies or load balancers are present. The solution architecture should incorporate defensive programming practices that validate all inputs before using them in critical operations such as URL generation, aligning with ATT&CK technique T1071.004 for application layer protocol manipulation. Network-level protections including WAF rules that monitor and filter suspicious header values can provide additional defense-in-depth measures to prevent exploitation of this vulnerability while maintaining proper application functionality.
This vulnerability demonstrates the importance of secure input handling in web applications, particularly when dealing with headers that are commonly manipulated by reverse proxies or load balancers. The flaw highlights how seemingly benign configuration elements can become attack vectors when proper validation mechanisms are absent from critical code paths. Organizations should conduct regular security assessments focusing on header manipulation and URL construction processes to identify similar vulnerabilities in their application stacks. The mitigation approach should include comprehensive testing of input validation mechanisms, implementation of automated security scanning for header-related issues, and adherence to secure coding practices that prioritize input sanitization over trust assumptions in network-layer information.