CVE-2023-45757 in bRPC
Summary
by MITRE • 10/25/2023
Security vulnerability in Apache bRPC <=1.6.0 on all platforms allows attackers to inject XSS code to the builtin rpcz page. An attacker that can send http request to bRPC server with rpcz enabled can inject arbitrary XSS code to the builtin rpcz page.
Solution (choose one of three): 1. upgrade to bRPC > 1.6.0, download link: https://dist.apache.org/repos/dist/release/brpc/1.6.1/ 2. If you are using an old version of bRPC and hard to upgrade, you can apply this patch: https://github.com/apache/brpc/pull/2411 3. disable rpcz feature
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Analysis
by VulDB Data Team • 11/02/2023
The vulnerability identified as CVE-2023-45757 affects Apache bRPC versions 1.6.0 and earlier, presenting a cross-site scripting vulnerability within the built-in rpcz monitoring page. This security flaw emerges when the rpcz feature is enabled on a bRPC server, creating an avenue for attackers to inject malicious JavaScript code that executes within the context of other users' browsers. The rpcz page serves as a diagnostic interface providing runtime statistics and information about the service, making it a valuable target for attackers seeking to exploit the system. The vulnerability specifically resides in how the rpcz page processes and displays user-provided input without adequate sanitization or encoding mechanisms, allowing malicious payloads to persist and execute when the page is accessed by legitimate users.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within the rpcz page handler. When attackers send HTTP requests containing malicious payloads to a bRPC server with rpcz enabled, the system fails to properly sanitize the input before incorporating it into the HTML response. This represents a classic cross-site scripting flaw categorized under CWE-79, which defines the condition where applications fail to properly encode output, allowing attackers to inject malicious scripts. The vulnerability exists in the server-side processing logic where user-controllable parameters are directly reflected in the web page without appropriate security measures such as HTML escaping or Content Security Policy enforcement. Attackers can leverage this weakness to execute arbitrary JavaScript code in the browser context of authenticated users, potentially leading to session hijacking, data exfiltration, or further exploitation of the compromised systems.
The operational impact of this vulnerability extends beyond simple script injection, as it enables attackers to establish persistent footholds within environments using vulnerable bRPC deployments. When the rpcz page is accessed by legitimate users, the injected JavaScript executes in their browsers, potentially allowing attackers to steal session cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users. The attack vector is particularly concerning because it requires minimal privileges to exploit - attackers only need to be able to send HTTP requests to a server with rpcz enabled, which is often a standard administrative function. This vulnerability undermines the security posture of distributed systems relying on bRPC for service communication, as it creates an attack surface that can be leveraged for reconnaissance and subsequent compromise of the broader service infrastructure. The implications are especially severe in enterprise environments where rpcz monitoring is enabled for debugging and operational purposes, as it transforms legitimate monitoring tools into potential attack vectors.
The recommended mitigation strategies provide multiple pathways for addressing this vulnerability while considering different deployment scenarios and upgrade constraints. The primary solution involves upgrading to bRPC version 1.6.1 or later, which includes proper input sanitization and output encoding fixes that resolve the XSS vulnerability. This upgrade path represents the most comprehensive solution as it addresses the root cause through proper code modifications and security hardening. For deployments where immediate upgrading is not feasible, applying the patch referenced in the GitHub pull request #2411 provides a targeted fix that addresses the specific input handling issue without requiring a full version upgrade. Alternatively, organizations can disable the rpcz feature entirely, which removes the attack surface by preventing access to the vulnerable monitoring interface. This approach is particularly suitable for environments where rpcz monitoring is not essential for operations or when other monitoring solutions are available. The choice of mitigation depends on organizational constraints, operational requirements, and risk tolerance levels, but all approaches align with standard security practices for addressing XSS vulnerabilities. The ATT&CK framework would categorize this vulnerability under T1566.001 for initial access through web application attacks, and potentially T1071.004 for application layer protocol usage, highlighting the need for proper input validation and output encoding as fundamental security controls.