CVE-2018-17031 in Gogs
Summary
by MITRE
In Gogs 0.11.53, an attacker can use a crafted .eml file to trigger MIME type sniffing, which leads to XSS, as demonstrated by Internet Explorer, because an "X-Content-Type-Options: nosniff" header is not sent.
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Analysis
by VulDB Data Team • 05/16/2023
The vulnerability CVE-2018-17031 affects Gogs version 0.11.53 and represents a critical cross-site scripting vulnerability that exploits MIME type sniffing behavior in web browsers. This flaw allows attackers to craft malicious .eml files that can bypass security mechanisms designed to prevent XSS attacks. The vulnerability specifically leverages the absence of the X-Content-Type-Options: nosniff header in HTTP responses, which is a crucial security measure for preventing content type confusion attacks. When Internet Explorer processes these crafted files, it performs MIME type sniffing that can lead to execution of malicious JavaScript code in the context of the victim's browser session.
The technical root cause of this vulnerability stems from improper content type handling within the Gogs web application. Without the X-Content-Type-Options: nosniff header, browsers are permitted to perform MIME type sniffing on content that is served with ambiguous or unspecified content types. This behavior creates an attack surface where malicious content can be interpreted as executable JavaScript rather than as benign email content. The vulnerability is particularly dangerous because it exploits the default behavior of Internet Explorer, which has historically been more aggressive in MIME type sniffing compared to other browsers. This makes the attack vector more likely to succeed in real-world scenarios where users may be browsing with older or less secure browser configurations.
The operational impact of this vulnerability extends beyond simple XSS exploitation, as it can enable attackers to perform a wide range of malicious activities including session hijacking, data theft, and privilege escalation within the Gogs environment. When an authenticated user opens a crafted .eml file, the malicious JavaScript code can execute with the privileges of that user, potentially allowing attackers to access private repositories, modify code, or even take control of user accounts. This vulnerability particularly affects organizations that rely on Gogs for code repository management, as it could enable attackers to compromise source code integrity and access sensitive development information. The attack requires minimal user interaction beyond opening the malicious file, making it particularly dangerous in phishing scenarios or when users are tricked into downloading and viewing compromised email attachments.
The vulnerability aligns with CWE-1004 which addresses insecure default conditions and specifically relates to the lack of proper content type handling in web applications. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 (Command and Scripting Interpreter: JavaScript) and T1566 (Phishing) as it enables both code execution and user deception techniques. Organizations should implement immediate mitigations including adding the X-Content-Type-Options: nosniff header to all HTTP responses, implementing proper content type validation for file uploads, and educating users about the risks of opening untrusted email attachments. Additionally, upgrading to Gogs versions that properly address this vulnerability is essential, as the issue affects the core web application functionality and represents a fundamental security flaw in the content handling mechanisms. The vulnerability demonstrates the critical importance of proper HTTP security headers and content type validation in preventing MIME type confusion attacks that can lead to severe security consequences.