CVE-2012-2686 in OpenSSL
Summary
by MITRE
crypto/evp/e_aes_cbc_hmac_sha1.c in the AES-NI functionality in the TLS 1.1 and 1.2 implementations in OpenSSL 1.0.1 before 1.0.1d allows remote attackers to cause a denial of service (application crash) via crafted CBC data.
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Analysis
by VulDB Data Team • 05/04/2021
The vulnerability identified as CVE-2012-2686 represents a critical denial of service flaw within the OpenSSL cryptographic library's implementation of AES-NI functionality. This issue specifically affects the TLS 1.1 and TLS 1.2 protocol implementations where the library employs hardware acceleration features for AES operations. The vulnerability manifests in the crypto/evp/e_aes_cbc_hmac_sha1.c file, which handles the CBC (Cipher Block Chaining) mode encryption combined with HMAC-SHA1 authentication for secure communication channels. The flaw occurs when OpenSSL processes specially crafted CBC data that triggers an improper handling of the cryptographic operations, leading to application crashes and complete service unavailability.
The technical root cause of this vulnerability lies in the insufficient validation of input data within the AES-NI accelerated code path for CBC-HMAC operations. When the TLS implementation receives malformed or specially crafted CBC data, the cryptographic processing routine fails to properly handle edge cases or invalid input sequences. This failure results in memory corruption or invalid pointer dereferences that cause the application to terminate abruptly. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it a significant threat to any system running affected OpenSSL versions. The issue is classified under CWE-125 as an out-of-bounds read, which is a common vector for denial of service attacks in cryptographic implementations.
The operational impact of CVE-2012-2686 extends beyond simple service disruption to potentially compromise the availability of critical infrastructure services. Web servers, email servers, and other network services that rely on OpenSSL for TLS encryption are vulnerable to this attack, which can be executed by sending maliciously crafted TLS handshake data to the target system. Attackers can exploit this vulnerability to repeatedly crash services, creating persistent denial of service conditions that can severely impact business operations and user access. The vulnerability affects all systems using OpenSSL versions 1.0.1 through 1.0.1c, making it widespread across many internet-facing services that were common during that time period. This type of vulnerability aligns with ATT&CK technique T1499.004, which describes denial of service through resource exhaustion or application crashes.
Mitigation strategies for CVE-2012-2686 require immediate deployment of OpenSSL patches and updates to versions 1.0.1d and later, which contain the necessary fixes to properly validate input data and prevent the crashes. System administrators should prioritize patching all affected systems, particularly those running web servers, mail servers, and other services that handle TLS connections. Organizations should also implement network monitoring to detect unusual traffic patterns that might indicate exploitation attempts. Additional defensive measures include configuring firewalls to limit TLS connection rates and implementing intrusion detection systems that can identify malformed TLS traffic. The vulnerability highlights the importance of thorough testing of cryptographic implementations, especially when hardware acceleration features are involved, as these optimizations can introduce complex failure modes that are difficult to predict and validate. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other cryptographic libraries and implementations that may be susceptible to similar flaws.