CVE-2005-0490 in cURL
Summary
by MITRE
Multiple stack-based buffer overflows in libcURL and cURL 7.12.1, and possibly other versions, allow remote malicious web servers to execute arbitrary code via base64 encoded replies that exceed the intended buffer lengths when decoded, which is not properly handled by (1) the Curl_input_ntlm function in http_ntlm.c during NTLM authentication or (2) the Curl_krb_kauth and krb4_auth functions in krb4.c during Kerberos authentication.
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Analysis
by VulDB Data Team • 07/05/2025
This vulnerability represents a critical stack-based buffer overflow in the popular cURL and libcURL libraries that affected version 7.12.1 and potentially other releases. The flaw arises from inadequate input validation during authentication processes when handling base64 encoded responses from malicious web servers. The vulnerability specifically impacts two authentication mechanisms within the cURL library stack. The first vulnerability occurs in the Curl_input_ntlm function located in the http_ntlm.c file during NTLM authentication, while the second vulnerability exists in the Curl_krb_kauth and krb4_auth functions within the krb4.c file during Kerberos authentication processes. Both scenarios involve the improper handling of base64 decoded data that exceeds intended buffer boundaries, creating opportunities for stack corruption and arbitrary code execution.
The technical implementation of this vulnerability exploits the fundamental weakness in how cURL processes authentication responses from remote web servers. During NTLM authentication, the Curl_input_ntlm function processes base64 encoded data without sufficient bounds checking, allowing malicious actors to craft specially crafted responses that exceed the allocated buffer space. Similarly, during Kerberos authentication, the Curl_krb_kauth and krb4_auth functions fail to properly validate the length of base64 decoded data, creating identical overflow conditions. The base64 decoding process itself does not inherently cause the issue, but rather the subsequent handling of the decoded data without proper size validation. This type of vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is categorized as a critical security weakness in software development practices. The vulnerability is particularly dangerous because it can be triggered remotely through web server responses, making it exploitable without requiring local system access.
The operational impact of this vulnerability extends far beyond simple code execution, as it represents a severe privilege escalation risk for systems utilizing cURL for web communications. Any application or service that relies on cURL for HTTP or HTTPS operations becomes vulnerable to remote code execution when communicating with malicious web servers. This includes web browsers, network monitoring tools, automated download applications, and system administration utilities that depend on cURL functionality. The attack vector is particularly insidious because it requires no user interaction or special privileges from the victim, as the malicious code execution occurs during normal authentication processes. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, though more accurately represents a direct binary exploitation scenario that could be leveraged in broader attack chains for privilege escalation and persistence. The vulnerability affects not just individual applications but entire ecosystems that depend on the underlying cURL library, potentially creating cascading security issues across multiple software platforms.
Mitigation strategies for this vulnerability require immediate patching of affected cURL and libcURL installations, as well as implementing network-level restrictions to prevent communication with untrusted web servers. Organizations should prioritize updating to versions of cURL that contain fixes for this specific buffer overflow issue, typically versions released after the vulnerability disclosure in 2005. Network administrators should consider implementing proxy servers or firewalls that can filter potentially malicious base64 encoded content during authentication processes. Application developers should review their code for direct or indirect dependencies on vulnerable cURL versions and ensure proper input validation is implemented at multiple layers. Additionally, monitoring systems should be configured to detect unusual authentication patterns or base64 encoded content that might indicate exploitation attempts. The fix typically involves implementing proper bounds checking and buffer size validation before processing decoded base64 data, ensuring that all authentication response handling includes adequate memory allocation and validation routines. This vulnerability highlights the importance of secure coding practices and the necessity of thorough input validation, particularly for authentication mechanisms that process external data streams.