CVE-2024-23826 is a medium severity vulnerability affecting the spbu_se_site, the website of the Department of System Programming at St. Petersburg State University. The vulnerability arises from improper resource allocation controls when authenticated users upload avatar images. Specifically, before the patch released on 2024-01-29, the system did not limit the length of the filename for uploaded avatars. An attacker could exploit this by submitting a filename with an excessively large Unicode string. On Windows operating systems, the server performs Unicode normalization using the NFKD form, which is computationally expensive. When processing a very large Unicode filename, this normalization process consumes excessive CPU and memory resources, leading to a denial of service (DoS) condition on the server. This vulnerability is categorized under CWE-770, which refers to allocation of resources without limits or throttling. The attack requires the user to be authenticated and to interact by uploading an avatar with a crafted filename. The CVSS v3.1 score is 6.8, reflecting a medium severity with network attack vector, low attack complexity, requiring privileges and user interaction, and impacting confidentiality, integrity, and availability primarily through availability impact (server DoS). No known exploits are reported in the wild as of the publication date. The vulnerability was fixed in the 2024.01.29 release by presumably adding filename length restrictions or improving normalization handling to prevent resource exhaustion.

For European organizations, the direct impact of this vulnerability is limited to those using the spbu_se_site platform or related software components from the St. Petersburg State University Department of System Programming. If such systems are deployed in European academic or research institutions, or integrated into internal tools, attackers with authenticated access could cause denial of service, disrupting availability of services. This could lead to temporary loss of access to critical academic or administrative web services, impacting productivity and potentially delaying research or educational activities. The vulnerability does not appear to allow remote code execution or data exfiltration, so confidentiality and integrity impacts are low. However, the denial of service could be leveraged as part of a broader attack chain or to cause reputational damage. Since exploitation requires authentication and user interaction, the threat is somewhat mitigated but still relevant in environments with many authenticated users. European organizations with Windows-based servers hosting the vulnerable software are at higher risk due to the Windows-specific nature of the Unicode normalization issue.

Organizations should immediately update spbu_se_site installations to version 2024.01.29 or later, which contains the fix for this vulnerability. If immediate patching is not possible, implement strict input validation and limit the maximum length of uploaded filenames at the application level to prevent excessively long Unicode strings. Additionally, monitor server resource usage for abnormal spikes during avatar uploads to detect potential exploitation attempts. Restrict avatar upload functionality to trusted users and consider adding CAPTCHA or other interaction controls to reduce automated abuse. On Windows servers, review Unicode normalization handling and consider applying OS-level mitigations or resource limits to prevent excessive CPU consumption. Regularly audit authentication and upload logs to identify suspicious activity. Finally, educate users about secure upload practices and the risks of uploading files with unusual filenames.