CVE-2008-1948 in gnutls
Summary
by MITRE
The _gnutls_server_name_recv_params function in lib/ext_server_name.c in libgnutls in gnutls-serv in GnuTLS before 2.2.4 does not properly calculate the number of Server Names in a TLS 1.0 Client Hello message during extension handling, which allows remote attackers to cause a denial of service (crash) or possibly execute arbitrary code via a zero value for the length of Server Names, which leads to a buffer overflow in session resumption data in the pack_security_parameters function, aka GNUTLS-SA-2008-1-1.
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability described in CVE-2008-1948 represents a critical buffer overflow flaw within the GnuTLS library's handling of TLS client hello messages. This issue specifically affects the _gnutls_server_name_recv_params function located in lib/ext_server_name.c, which processes server name indication extensions during the TLS handshake process. The flaw manifests when the library encounters a malformed TLS 1.0 Client Hello message containing a zero-length server name field, creating a scenario where the application fails to properly validate input parameters before proceeding with memory operations. This particular vulnerability falls under the CWE-121 category of stack-based buffer overflow, where insufficient bounds checking allows attackers to manipulate memory layout during extension processing. The vulnerability impacts the gnutls-serv component of GnuTLS, making it particularly dangerous for servers that rely on this cryptographic library for secure communications.
The technical implementation of this vulnerability stems from improper handling of the server name length field within the TLS extension parsing logic. When a malicious client sends a Client Hello message with a zero value for the server name length parameter, the gnutls library fails to validate this input before attempting to process the subsequent data. This validation failure leads to a buffer overflow condition in the pack_security_parameters function, which is responsible for preparing session resumption data. The overflow occurs because the library calculates memory allocation based on the malformed length value, resulting in insufficient buffer space for the actual data being copied. This type of vulnerability directly maps to ATT&CK technique T1203, which involves exploitation of input validation flaws to achieve arbitrary code execution or system compromise. The flaw exists in the protocol implementation layer where the library should have performed proper bounds checking before proceeding with memory operations.
The operational impact of CVE-2008-1948 extends beyond simple denial of service to potentially enable remote code execution, making it a severe threat to systems relying on GnuTLS for secure communications. When exploited, the vulnerability can cause service crashes that disrupt legitimate user access, but more concerning is the potential for attackers to leverage the buffer overflow for privilege escalation or arbitrary code execution on vulnerable systems. This makes the vulnerability particularly dangerous in server environments where GnuTLS is used for HTTPS, SMTPS, or other secure communication protocols. The attack vector requires minimal privileges as the exploit can be launched from a remote location, making it suitable for widespread exploitation. Systems running GnuTLS versions prior to 2.2.4 are at risk, particularly web servers, mail servers, and any application that utilizes the vulnerable cryptographic library for secure session management. The vulnerability affects both the server-side implementation and client-side applications that process TLS handshake messages, creating a broad attack surface for potential exploitation.
Mitigation strategies for CVE-2008-1948 require immediate deployment of the patched GnuTLS version 2.2.4 or later, which includes proper bounds checking for server name length parameters. Organizations should implement network segmentation and monitoring to detect anomalous TLS handshake patterns that might indicate exploitation attempts. The fix involves strengthening input validation in the _gnutls_server_name_recv_params function to ensure that server name length values are properly validated before memory allocation occurs. Security teams should also consider implementing intrusion detection systems that can identify malformed TLS Client Hello messages with zero-length server name fields. Additionally, regular security audits of cryptographic library implementations should be conducted to identify similar validation flaws in other components. The vulnerability highlights the importance of proper input validation in cryptographic implementations and demonstrates how seemingly minor parsing errors can result in critical security vulnerabilities. Organizations should also review their certificate management practices and ensure that all systems using GnuTLS are updated to versions that address this specific buffer overflow condition. The remediation process should include thorough testing of patched implementations to ensure that legitimate functionality remains intact while eliminating the security risk associated with malformed TLS handshake processing.