CVE-2026-2878 identifies an insufficient entropy vulnerability (CWE-331) in the RadAsyncUpload component of Progress Software's Telerik UI for ASP.NET AJAX versions prior to 2026.1.225. The vulnerability stems from the generation of temporary file identifiers that are predictable because they are based on a combination of the current timestamp and the original filename. This predictability reduces the randomness (entropy) of the identifier, making it feasible for an attacker to guess or cause collisions with existing temporary file identifiers. Such collisions can lead to file content tampering during the upload process, where an attacker may overwrite or inject malicious content into files being uploaded by other users. The vulnerability requires user interaction (uploading files) and has a high attack complexity, meaning exploitation is not trivial but possible under certain conditions. No privileges or authentication are required to attempt exploitation, and the scope is limited to the integrity of uploaded files, with no direct impact on confidentiality or availability. No patches were linked in the provided data, but the vendor has reserved the CVE and published the vulnerability details. No known exploits are reported in the wild yet, but the flaw represents a significant risk for web applications relying on Telerik UI for file uploads, especially in environments where file integrity is critical.

The primary impact of CVE-2026-2878 is on the integrity of files uploaded via the RadAsyncUpload component in Telerik UI for ASP.NET AJAX. Successful exploitation can allow attackers to tamper with or replace uploaded files, potentially injecting malicious payloads or corrupting data. This can lead to downstream security issues such as malware distribution, unauthorized code execution if the uploaded files are processed or executed by the server, or disruption of business processes relying on file uploads. Since the vulnerability does not affect confidentiality or availability directly, the risk is focused on data integrity. Organizations that rely on Telerik UI for handling sensitive or critical file uploads—such as financial institutions, healthcare providers, and enterprises with document management systems—face increased risk. The requirement for user interaction limits mass exploitation but targeted attacks against specific users or systems remain feasible. The medium CVSS score (5.3) reflects the moderate severity due to the attack complexity and limited scope but should not lead to complacency given the potential consequences of file tampering.

To mitigate CVE-2026-2878, organizations should upgrade Telerik UI for ASP.NET AJAX to version 2026.1.225 or later, where the vulnerability is addressed by improving the entropy of temporary file identifiers. In the absence of an immediate patch, developers should implement custom logic to generate truly random and unpredictable temporary file names or identifiers, avoiding reliance on timestamps and filenames alone. Additionally, enforcing strict server-side validation and integrity checks on uploaded files can detect tampering attempts. Employing file scanning for malware and verifying file hashes before processing can reduce risk. Restricting file upload permissions and isolating upload directories can limit the impact of any tampering. Monitoring upload logs for unusual patterns or collisions can help detect exploitation attempts early. Finally, educating users about safe upload practices and limiting upload functionality to trusted users can reduce exposure.