CVE-2011-4128 in gnutls
Summary
by MITRE
Buffer overflow in the gnutls_session_get_data function in lib/gnutls_session.c in GnuTLS 2.12.x before 2.12.14 and 3.x before 3.0.7, when used on a client that performs nonstandard session resumption, allows remote TLS servers to cause a denial of service (application crash) via a large SessionTicket.
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Analysis
by VulDB Data Team • 11/28/2021
The vulnerability identified as CVE-2011-4128 represents a critical buffer overflow condition within the GnuTLS library implementation that affects versions prior to 2.12.14 and 3.0.7. This flaw specifically targets the gnutls_session_get_data function located in lib/gnutls_session.c, where improper handling of session data during nonstandard session resumption scenarios creates an exploitable condition. The vulnerability manifests when a remote TLS server crafts a maliciously large SessionTicket that exceeds the allocated buffer space, leading to memory corruption and subsequent application instability.
The technical exploitation of this vulnerability occurs during the TLS session resumption process where client applications using GnuTLS attempt to process session tickets received from servers. When a client encounters a SessionTicket that exceeds the expected buffer size during the gnutls_session_get_data function execution, the program writes beyond the allocated memory boundaries, causing stack corruption or heap overflow conditions. This buffer overflow directly violates the principles of memory safety and can be classified under CWE-121 as a stack-based buffer overflow, while also demonstrating characteristics of CWE-122 which relates to heap-based buffer overflows. The vulnerability specifically impacts the TLS client-side implementation where session resumption is performed, making it particularly dangerous in environments where clients frequently reconnect to multiple TLS servers.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attack vectors. While the primary effect is application crash and denial of service, the buffer overflow condition creates opportunities for attackers to execute arbitrary code or escalate privileges depending on the memory layout and system configuration. The vulnerability affects any application that utilizes the affected GnuTLS library versions for TLS client operations, including web browsers, email clients, and network security tools that rely on secure communication protocols. Attackers can leverage this weakness by establishing a TLS connection to a malicious server that sends oversized SessionTickets, causing legitimate client applications to crash and potentially allowing further exploitation if proper memory protection mechanisms are not in place.
Mitigation strategies for CVE-2011-4128 primarily focus on immediate patching of affected GnuTLS library versions to the secure releases 2.12.14 and 3.0.7 respectively. System administrators should prioritize updating all affected applications and systems that utilize vulnerable GnuTLS implementations, particularly those handling TLS client connections. Additional defensive measures include implementing network-level controls such as intrusion detection systems that can identify and block suspicious SessionTicket patterns, configuring applications to limit session ticket sizes, and enabling memory protection features like stack canaries and address space layout randomization. The vulnerability also highlights the importance of proper input validation and bounds checking in cryptographic libraries, aligning with ATT&CK technique T1059.007 for command and scripting interpreter usage and T1499.004 for network disruption. Organizations should also consider implementing application whitelisting and monitoring for abnormal application behavior that may indicate exploitation attempts, while maintaining comprehensive logging of TLS session activities to detect potential attacks against the vulnerable library functions.