CVE-2026-27480 in Static Web Server
Summary
by MITRE • 02/21/2026
Static Web Server (SWS) is a production-ready web server suitable for static web files or assets. In versions 2.1.0 through 2.40.1, a timing-based username enumeration vulnerability in Basic Authentication allows attackers to identify valid users by exploiting early responses for invalid usernames, enabling targeted brute-force or credential-stuffing attacks. SWS checks whether a username exists before verifying the password, causing valid usernames to follow a slower code path (e.g., bcrypt hashing) while invalid usernames receive an immediate 401 response. This timing discrepancy allows attackers to enumerate valid accounts by measuring response-time differences. This issue has been fixed in version 2.41.0.
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Analysis
by VulDB Data Team • 02/21/2026
The vulnerability described in CVE-2026-27480 represents a critical timing-based username enumeration flaw within the Static Web Server (SWS) authentication mechanism. This issue affects versions 2.1.0 through 2.40.1 and specifically targets the Basic Authentication implementation that SWS employs for securing static web assets. The fundamental problem lies in the server's response behavior during authentication attempts, where the timing characteristics of the response vary significantly based on whether the provided username exists in the system. This timing inconsistency creates an exploitable side-channel that adversaries can leverage to determine valid user accounts through careful measurement of server response times.
The technical implementation of this vulnerability stems from SWS's flawed authentication logic where the server performs username validation before password verification. When an attacker submits a login request with an invalid username, the system immediately returns a 401 Unauthorized response without performing any password hashing operations. However, when a valid username is provided, the server must proceed through the complete authentication pipeline including password verification using bcrypt hashing, which is computationally intensive and introduces measurable delays. This differential response time creates a timing-based oracle that directly reveals the existence of legitimate accounts within the system. The vulnerability aligns with CWE-208, which specifically addresses timing information exposure, and represents a classic example of how implementation details can create security weaknesses even in seemingly straightforward authentication mechanisms.
The operational impact of this vulnerability extends beyond simple account enumeration, creating a foundation for more sophisticated attacks including targeted brute-force attempts and credential-stuffing campaigns. Attackers can systematically test usernames and measure response times to distinguish between valid and invalid accounts, effectively bypassing traditional rate-limiting protections that might not account for timing-based enumeration techniques. This vulnerability particularly affects environments where SWS serves sensitive static assets or where user account management is critical, as it allows unauthorized parties to build comprehensive lists of valid users before launching more destructive attacks. The timing discrepancy becomes even more pronounced under load conditions, making the enumeration process faster and more reliable for attackers. Organizations using SWS in production environments face significant risk of account compromise and potential unauthorized access to protected static content.
The mitigation strategy for CVE-2026-27480 requires immediate upgrade to SWS version 2.41.0, which addresses the timing-based enumeration issue by implementing constant-time authentication logic. This fix ensures that the server responds with consistent timing regardless of whether the username exists in the system, eliminating the timing oracle that enabled enumeration attacks. Additionally, security teams should implement comprehensive monitoring for unusual authentication patterns and response time variations that might indicate active enumeration attempts. Organizations should also consider implementing additional authentication layers including multi-factor authentication, rate limiting with randomized delays, and account lockout mechanisms to provide defense in depth. The vulnerability demonstrates the importance of considering timing characteristics in security implementations and highlights the need for thorough security testing that includes side-channel analysis. This issue also relates to ATT&CK technique T1110.001, which covers credential brute force through password guessing, and emphasizes the necessity of implementing proper authentication timing controls to prevent such attacks.