CVE-2017-7805 in Directory Server Enterprise Edition
Summary
by MITRE
During TLS 1.2 exchanges, handshake hashes are generated which point to a message buffer. This saved data is used for later messages but in some cases, the handshake transcript can exceed the space available in the current buffer, causing the allocation of a new buffer. This leaves a pointer pointing to the old, freed buffer, resulting in a use-after-free when handshake hashes are then calculated afterwards. This can result in a potentially exploitable crash. This vulnerability affects Firefox < 56, Firefox ESR < 52.4, and Thunderbird < 52.4.
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Analysis
by VulDB Data Team • 05/26/2023
The vulnerability described in CVE-2017-7805 represents a critical use-after-free condition within the TLS 1.2 handshake implementation of Mozilla Firefox and Thunderbird applications. This flaw occurs during the cryptographic handshake process where the software maintains a transcript of all handshake messages to generate cryptographic hashes that ensure the integrity of the communication channel. The underlying issue stems from improper memory management when handling large handshake transcripts that exceed the capacity of the initially allocated buffer space. When this overflow occurs, the system allocates a new buffer while leaving references to the previously freed memory location, creating a scenario where subsequent operations attempt to access deallocated memory regions.
The technical execution of this vulnerability involves the TLS 1.2 handshake protocol where the software maintains a running transcript of all handshake messages to compute cryptographic hashes for authentication purposes. When the handshake transcript grows beyond the allocated buffer boundaries, the system reallocates memory to accommodate the additional data. However, the implementation fails to properly update all references to the old memory location, leaving pointers pointing to freed memory. This memory management error creates a use-after-free condition that can be exploited by attackers to execute arbitrary code or cause application crashes. The vulnerability specifically impacts the cryptographic hash calculation functions that rely on the handshake transcript data, making it particularly dangerous as it occurs during the critical security handshake phase.
From an operational perspective, this vulnerability presents a significant risk to users of affected software versions as it can be exploited to achieve remote code execution through carefully crafted TLS handshake messages. Attackers can potentially deliver malicious TLS responses that trigger the buffer overflow condition, leading to memory corruption and potential exploitation. The impact extends beyond simple crashes to include full system compromise when successfully exploited, making this vulnerability particularly concerning for security-conscious environments. The affected products include Firefox versions prior to 56, Firefox ESR versions prior to 52.4, and Thunderbird versions prior to 52.4, representing a substantial user base that required immediate patching. This vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software implementations, and can be mapped to ATT&CK technique T1059.007 for remote code execution through application vulnerabilities.
The mitigation strategy for CVE-2017-7805 requires immediate deployment of security patches from Mozilla that address the memory management issues in the TLS handshake implementation. Organizations should prioritize updating all affected Firefox and Thunderbird installations to versions 56.0 or later for Firefox, 52.4 or later for Firefox ESR, and 52.4 or later for Thunderbird. Additionally, network administrators should monitor for any attempts to exploit this vulnerability through TLS handshake manipulation and implement network-level controls to detect suspicious traffic patterns. The patch addresses the root cause by ensuring proper memory management during buffer reallocation and updating all references to prevent access to freed memory locations. Security teams should also consider implementing additional monitoring and alerting mechanisms to detect potential exploitation attempts, as the vulnerability can be leveraged for privilege escalation and persistent access to compromised systems.