CVE-2026-26717 identifies a cryptographic verification vulnerability in the OpenFUN Richie Learning Management System (LMS), specifically in the source file src/richie/apps/courses/api.py. The vulnerability arises because the application uses the standard equality operator (==) to compare HMAC signatures during the execution of the sync_course_run_from_request function. This comparison is not performed in constant time, which means the time taken to compare two signatures can vary depending on how many bytes match. Remote attackers can exploit this timing discrepancy by sending multiple crafted requests and measuring the response times to gradually infer the correct HMAC signature. By successfully forging a valid signature, attackers can bypass authentication controls that protect course synchronization operations. This can lead to unauthorized access or manipulation of course data within the LMS. The vulnerability does not require prior authentication or user interaction, increasing its risk. Although no public exploits or patches are currently available, the flaw represents a classic timing attack vector against HMAC verification, a well-known cryptographic weakness when constant-time comparison is not used. The absence of a CVSS score suggests this is a newly published issue, but the impact on confidentiality and integrity is significant. The vulnerability affects all versions of OpenFUN Richie LMS that use this verification method, though specific affected versions are not listed. Mitigation involves replacing the vulnerable comparison with a constant-time comparison function to prevent timing side-channel leakage.

The primary impact of CVE-2026-26717 is the potential for remote attackers to bypass authentication mechanisms by forging valid HMAC signatures. This allows unauthorized access to sensitive LMS functions, particularly those related to course synchronization. Attackers could manipulate course data, inject unauthorized content, or disrupt normal LMS operations, potentially affecting the integrity and availability of educational content. The confidentiality of course synchronization requests may also be compromised if attackers can impersonate legitimate requests. Organizations relying on OpenFUN Richie LMS for educational delivery or training risk data tampering, unauthorized access, and service disruption. The ease of exploitation is moderate since it requires precise timing measurements but no authentication or user interaction, making automated attacks feasible. The scope includes all installations of OpenFUN Richie LMS using the vulnerable code path, which may be significant in educational institutions, corporate training environments, and other sectors using this LMS. Although no known exploits are reported, the vulnerability presents a credible risk that could be leveraged in targeted attacks or by opportunistic threat actors.

To mitigate CVE-2026-26717, organizations should immediately review the HMAC signature verification implementation in OpenFUN Richie LMS, specifically the sync_course_run_from_request function. Replace the non-constant time equality operator (==) with a constant-time comparison function designed to prevent timing side-channel attacks, such as hmac.compare_digest in Python. If a patch from the vendor becomes available, apply it promptly. In the absence of an official patch, consider implementing custom constant-time comparison logic or using cryptographic libraries that provide secure HMAC verification. Additionally, monitor LMS logs for unusual or repeated requests to course synchronization endpoints that could indicate timing attack attempts. Employ network-level protections such as rate limiting and anomaly detection to reduce the feasibility of timing measurements by attackers. Educate developers and security teams about the importance of constant-time comparisons in cryptographic operations to prevent similar vulnerabilities. Finally, maintain regular backups and have incident response plans ready in case of exploitation.