CVE-2018-1312 in HTTP Server
Summary
by MITRE
In Apache httpd 2.2.0 to 2.4.29, when generating an HTTP Digest authentication challenge, the nonce sent to prevent reply attacks was not correctly generated using a pseudo-random seed. In a cluster of servers using a common Digest authentication configuration, HTTP requests could be replayed across servers by an attacker without detection.
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Analysis
by VulDB Data Team • 02/24/2023
The vulnerability identified as CVE-2018-1312 affects Apache HTTP Server versions ranging from 2.2.0 through 2.4.29 and represents a critical flaw in the implementation of HTTP Digest authentication mechanisms. This issue stems from insufficient randomness in the nonce generation process, which serves as a cryptographic element designed to prevent replay attacks in the digest authentication protocol. The nonce is intended to be a unique value that changes with each authentication challenge, making it difficult for attackers to reuse successful authentication attempts across different server instances or time periods. When multiple servers in a load-balanced or clustered environment share the same Digest authentication configuration, the predictable nature of the nonce generation creates a significant security gap that undermines the fundamental security assumptions of the digest authentication mechanism.
The technical flaw manifests in the pseudo-random number generation algorithm used by Apache httpd when creating nonce values for HTTP Digest authentication challenges. This weakness allows attackers to predict or reproduce nonce values that should be cryptographically random and unique for each authentication attempt. The vulnerability specifically impacts clustered server environments where multiple Apache instances share identical authentication configurations, enabling an attacker to capture a valid authentication exchange and replay it against a different server instance within the same cluster without detection. This cross-server replay capability occurs because the nonce values generated by different servers in the cluster are either identical or follow predictable patterns, eliminating the effectiveness of the replay protection mechanism that nonce values are designed to provide.
The operational impact of CVE-2018-1312 extends beyond simple authentication bypass scenarios, creating potential for credential compromise and unauthorized access to protected resources across multiple server instances. Attackers can exploit this vulnerability to gain unauthorized access to web applications and services that rely on HTTP Digest authentication, particularly in environments where server clustering is implemented for scalability or high availability purposes. The vulnerability affects systems where multiple Apache httpd servers operate under the same authentication realm, making it particularly dangerous in enterprise environments with distributed web applications. The risk is amplified when considering that digest authentication is often used for protecting sensitive internal resources, API endpoints, and administrative interfaces where unauthorized access could lead to data breaches, system compromise, or further lateral movement within the network infrastructure.
Organizations affected by this vulnerability should implement immediate mitigations including upgrading to Apache httpd versions 2.4.30 or later, where the nonce generation has been corrected to use proper cryptographic random number generation. System administrators should also consider implementing additional security controls such as enforcing HTTPS for all authentication exchanges, implementing additional authentication layers, or migrating from HTTP Digest authentication to more secure alternatives such as HTTP Basic authentication over TLS, OAuth, or token-based authentication mechanisms. The vulnerability aligns with CWE-330 use of insufficent entropy and represents a failure in proper cryptographic implementation that could be categorized under ATT&CK technique T1110.003 for credential access through brute force or password guessing. Security teams should conduct comprehensive audits of their Apache configurations to identify all instances of HTTP Digest authentication and ensure that proper randomization is implemented across all server instances in clustered environments.