CVE-2005-3310 in phpBB
Summary
by MITRE
Interpretation conflict in phpBB 2.0.17, with remote avatars and avatar uploading enabled, allows remote authenticated users to inject arbitrary web script or HTML via an HTML file with a GIF or JPEG file extension, which causes the HTML to be executed by a victim who views the file in Internet Explorer, which renders malformed image types as HTML, enabling cross-site scripting (XSS) attacks. NOTE: it could be argued that this vulnerability is due to a design flaw in Internet Explorer (CVE-2005-3312) and the proper fix should be in that browser; if so, then this should not be treated as a vulnerability in phpBB.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 07/11/2019
The vulnerability described in CVE-2005-3310 represents a sophisticated cross-site scripting attack vector that exploits a fundamental mismatch between web application security practices and browser rendering behaviors. This flaw exists within phpBB version 2.0.17 where the application fails to properly validate file extensions when processing user-uploaded avatars, creating an avenue for malicious actors to bypass security controls through carefully crafted file naming conventions. The vulnerability specifically manifests when both remote avatars and avatar uploading features are enabled, establishing a critical attack surface that requires only authenticated user access to exploit effectively.
The technical exploitation mechanism leverages a well-known rendering inconsistency in Internet Explorer where the browser attempts to render malformed image files as HTML content when encountering certain file format discrepancies. An attacker can upload a malicious HTML file with a GIF or JPEG extension, which phpBB processes without proper validation of the actual file content. When another user views this avatar in Internet Explorer, the browser's rendering engine interprets the file as an image but inadvertently executes embedded HTML code, creating a persistent cross-site scripting vulnerability. This behavior aligns with CWE-79, which categorizes cross-site scripting vulnerabilities as weaknesses in input validation and output encoding, specifically addressing the improper handling of untrusted data in web applications.
The operational impact of this vulnerability extends beyond simple script injection, as it enables attackers to perform session hijacking, defacement of user profiles, and potential data exfiltration from victim browsers. The attack requires minimal privileges since it only necessitates authenticated access to upload files, making it particularly dangerous in environments where user permissions are not strictly enforced. The vulnerability's persistence is enhanced by the fact that the malicious content is stored server-side and executed each time users view affected profiles, creating a continuous attack vector that can compromise multiple users over time. Security professionals should note that this vulnerability demonstrates the critical importance of proper file type validation and the inherent risks of trusting file extensions without content verification.
The remediation approach for this vulnerability requires implementing strict file validation mechanisms that examine actual file content rather than relying solely on extensions, a principle aligned with ATT&CK technique T1078 which addresses legitimate credentials usage and privilege escalation through application flaws. phpBB administrators should disable remote avatar functionality or implement robust content validation that verifies file signatures and MIME types before processing uploads. The vulnerability highlights the need for comprehensive input sanitization and output encoding practices, emphasizing that security controls must be implemented at multiple layers to prevent such interpretation conflicts between application logic and browser behavior. Organizations should also consider implementing web application firewalls and content security policies to provide additional protection against similar vulnerabilities that exploit browser rendering inconsistencies.