CVE-2009-0590 in OpenSSL
Summary
by MITRE
The ASN1_STRING_print_ex function in OpenSSL before 0.9.8k allows remote attackers to cause a denial of service (invalid memory access and application crash) via vectors that trigger printing of a (1) BMPString or (2) UniversalString with an invalid encoded length.
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Analysis
by VulDB Data Team • 08/31/2019
The vulnerability identified as CVE-2009-0590 represents a critical denial of service flaw within the OpenSSL cryptographic library affecting versions prior to 0.9.8k. This vulnerability specifically targets the ASN1_STRING_print_ex function which is responsible for formatting and printing ASN.1 string types during certificate processing and other cryptographic operations. The flaw manifests when the function encounters malformed BMPString or UniversalString data structures with invalid encoded length values, creating a scenario where the application attempts to access invalid memory locations during the printing process.
The technical implementation of this vulnerability stems from inadequate input validation within the ASN1_STRING_print_ex function. When processing ASN.1 strings, the function does not properly verify the integrity of the encoded length field before attempting to access the associated data buffer. This weakness allows attackers to craft malicious certificates or data structures containing malformed BMPString or UniversalString elements with deliberately corrupted length fields. The improper validation causes the function to calculate memory access addresses based on invalid length values, leading to invalid memory dereferences and subsequent application crashes.
From an operational perspective, this vulnerability poses significant risks to systems relying on OpenSSL for secure communications, particularly those handling X.509 certificates and other ASN.1 encoded data. Attackers can exploit this flaw by presenting specially crafted certificates or data streams to vulnerable applications, causing them to crash and potentially leading to service disruption. The impact extends beyond simple denial of service as the vulnerability can affect web servers, email servers, and any application that processes certificate data through OpenSSL. This represents a classic example of a buffer over-read condition that can be leveraged for remote exploitation without requiring authentication or privileged access.
The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions in software implementations, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. Organizations using affected OpenSSL versions face substantial risk of service interruption and potential availability compromise, particularly in environments where certificate validation is critical for security operations. The vulnerability demonstrates the importance of proper input validation in cryptographic libraries and highlights how seemingly minor implementation flaws can result in significant security implications.
Mitigation strategies for CVE-2009-0590 require immediate patching of all affected OpenSSL installations to version 0.9.8k or later. System administrators should conduct comprehensive inventory checks to identify all systems running vulnerable OpenSSL versions and implement urgent security updates. Additionally, network monitoring should be enhanced to detect potential exploitation attempts through malformed certificate data. Organizations may also consider implementing certificate validation policies that reject certificates with malformed string encodings as an additional defensive measure. The vulnerability underscores the necessity of maintaining up-to-date cryptographic libraries and the importance of thorough security testing for cryptographic implementations.