CVE-2026-40496 in freescout
Summary
by MITRE • 04/21/2026
FreeScout is a free self-hosted help desk and shared mailbox. Prior to version 1.8.213, attachment download tokens are generated using a weak and predictable formula: `md5(APP_KEY + attachment_id + size)`. Since attachment_id is sequential and size can be brute-forced in a small range, an unauthenticated attacker can forge valid tokens and download any private attachment without credentials. Version 1.8.213 fixes the issue.
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Analysis
by VulDB Data Team • 05/10/2026
The vulnerability in FreeScout affects the attachment download token generation mechanism, creating a critical security weakness that undermines the application's access control measures. This flaw exists in versions prior to 1.8.213 where the system employs a predictable hashing algorithm to generate tokens for accessing private attachments. The token formula md5(APP_KEY + attachment_id + size) creates a deterministic system where attackers can compute valid tokens without proper authentication. The attachment_id field follows a sequential pattern, making it easily enumerable, while the size parameter operates within a limited range that allows for brute force attacks. This predictable token generation directly violates security principles outlined in CWE-330, which addresses the use of weak random number generators and predictable cryptographic operations. The vulnerability creates a path for unauthorized access to sensitive data through the principle of least privilege violation, where users without proper authentication can bypass access controls to download private attachments.
The technical implementation of this vulnerability stems from the insecure use of cryptographic functions and predictable data patterns in the token generation process. The md5 hashing algorithm, while not inherently broken for all purposes, becomes vulnerable when combined with predictable inputs such as sequential attachment identifiers and constrained size parameters. This weakness aligns with ATT&CK technique T1213.002, which covers data from local systems, specifically targeting the exploitation of predictable token generation mechanisms. The sequential nature of attachment_id values combined with the limited range of size parameters creates a brute force attack surface that allows attackers to systematically compute valid tokens. The vulnerability demonstrates poor entropy in the token generation process, as the combination of APP_KEY, attachment_id, and size creates a deterministic output that can be reverse-engineered by an attacker with minimal computational resources. This weakness represents a fundamental flaw in the application's security architecture and violates the core principle that access tokens should be unpredictable and resistant to forgery.
The operational impact of this vulnerability extends beyond simple unauthorized file access, creating potential risks for sensitive data exposure and privacy violations. An attacker can systematically download private attachments including confidential communications, customer data, and potentially sensitive business information without requiring authentication. This vulnerability affects the integrity and confidentiality of the help desk system, potentially exposing personal identifiable information and business-critical documents. The attack vector is particularly concerning as it requires no authentication credentials and can be automated using simple scripting techniques. The vulnerability creates a persistent threat where attackers can repeatedly access private attachments over time, potentially leading to data breaches and compliance violations. Organizations using affected versions of FreeScout face risks of regulatory penalties under data protection laws such as GDPR, CCPA, and HIPAA, depending on the nature of the data being stored. The vulnerability also impacts the trust relationship between users and the system, as it undermines the security guarantees provided by the application's access control mechanisms.
Mitigation strategies for this vulnerability require immediate patching to version 1.8.213 or later, which implements proper token generation mechanisms using cryptographically secure random number generators. Organizations should also implement additional security controls such as rate limiting on attachment download requests to prevent automated brute force attacks. The fix should ensure that tokens are generated using secure random values that cannot be predicted or reverse-engineered through knowledge of sequential identifiers. Security teams should conduct thorough audits of all token generation mechanisms within the application to identify similar vulnerabilities in other components. The implementation of proper access controls and audit logging for attachment downloads can help detect unauthorized access attempts. Additionally, organizations should consider implementing multi-factor authentication and network-level access controls to provide defense in depth. The vulnerability highlights the importance of following secure coding practices and conducting regular security assessments to identify cryptographic weaknesses that could be exploited by attackers. Organizations should also establish incident response procedures to handle potential data exposure events that may result from this vulnerability, including notification requirements for affected users and regulatory compliance measures.