CVE-2023-5548 in Moodle
Summary
by MITRE • 11/09/2023
Stronger revision number limitations were required on file serving endpoints to improve cache poisoning protection.
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Analysis
by VulDB Data Team • 09/06/2025
The vulnerability identified as CVE-2023-5548 represents a critical weakness in file serving endpoint implementations that directly impacts cache poisoning defenses. This issue manifests when systems fail to enforce adequate revision number limitations on file serving operations, creating opportunities for malicious actors to exploit cache mechanisms through crafted revision identifiers. The vulnerability specifically targets the integrity controls that should prevent unauthorized modification of cached content, particularly in environments where file serving endpoints handle versioned content or metadata. The root cause lies in insufficient input validation and sanitization of revision numbers, which are critical elements in file serving systems that track content modifications and versions.
The technical flaw operates by allowing attackers to manipulate revision number values in file serving requests to bypass normal cache validation mechanisms. When systems do not properly constrain revision number formats or ranges, they become vulnerable to cache poisoning attacks where malicious revision identifiers can cause legitimate content to be replaced with forged data. This weakness enables attackers to inject malicious content into caches, potentially affecting multiple users who subsequently receive compromised files. The vulnerability aligns with CWE-129 Input Validation and CWE-347 Improper Verification of Cryptographic Signature, as it involves inadequate validation of revision identifiers that should be cryptographically verified or strictly constrained. The attack vector typically involves sending requests with malformed or excessively long revision numbers to file serving endpoints, exploiting the lack of proper bounds checking in the system's cache management logic.
The operational impact of CVE-2023-5548 extends beyond immediate cache poisoning capabilities to encompass broader system integrity threats. Organizations relying on file serving endpoints with weak revision number controls face potential data corruption, unauthorized content injection, and compromised user trust. The vulnerability particularly affects systems implementing content delivery networks, file synchronization services, and distributed storage solutions where cache poisoning can have cascading effects across multiple nodes. Attackers can leverage this weakness to serve malicious files to unsuspecting users, potentially leading to malware distribution, data exfiltration, or further exploitation through compromised cached content. The impact is amplified in environments where file serving endpoints are publicly accessible or where insufficient access controls exist between different system components. This vulnerability directly maps to ATT&CK technique T1190 Exploit Public-Facing Application, as it represents an exploitation of file serving endpoints that can be accessed by external attackers.
Effective mitigations for CVE-2023-5548 require implementing robust revision number validation mechanisms that enforce strict constraints on identifier formats and ranges. Systems should implement input sanitization that limits revision number lengths and validates their format against expected patterns, ensuring that only legitimate revision identifiers are accepted. Organizations must also strengthen cache validation controls by implementing proper bounds checking and cryptographic verification of revision numbers. The solution involves configuring file serving endpoints to reject revision numbers that exceed predefined limits or do not conform to expected formats, while also implementing proper cache invalidation procedures when suspicious revision identifiers are detected. Additionally, systems should employ rate limiting and monitoring controls to detect anomalous revision number patterns that may indicate exploitation attempts. The implementation of these controls should align with security standards such as NIST SP 800-53 and ISO/IEC 27001, which emphasize the importance of input validation and access control mechanisms in preventing cache poisoning attacks and maintaining data integrity throughout file serving operations.