CVE-2016-0777 in Mac OS X
Summary
by MITRE
The resend_bytes function in roaming_common.c in the client in OpenSSH 5.x, 6.x, and 7.x before 7.1p2 allows remote servers to obtain sensitive information from process memory by requesting transmission of an entire buffer, as demonstrated by reading a private key.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2016-0777 represents a critical information disclosure flaw in OpenSSH client implementations across multiple versions including 5.x, 6.x, and 7.x before 7.1p2. This vulnerability specifically affects the resend_bytes function within the roaming_common.c file, which is responsible for handling client-side roaming functionality. The flaw stems from improper memory handling during buffer transmission processes, creating a pathway for malicious remote servers to extract sensitive data from the client's memory space. This vulnerability operates under the principle of memory disclosure attacks where an attacker can manipulate the client to transmit portions of its memory buffer, potentially exposing confidential information including private cryptographic keys.
The technical implementation of this vulnerability involves the resend_bytes function's inadequate boundary checking and memory management when processing buffer requests. When a remote server initiates a transmission request that triggers this function, the client fails to properly validate the buffer parameters, allowing the attacker to specify memory regions that should not be accessible. This flaw is categorized under CWE-200 as "Information Exposure" and more specifically relates to CWE-125 as "Out-of-bounds Read" since the function reads memory locations beyond its intended boundaries. The vulnerability manifests when the client processes a request that causes it to transmit an entire buffer rather than the intended data, thereby exposing process memory contents to the remote server.
The operational impact of CVE-2016-0777 is severe and far-reaching within the cybersecurity landscape. An attacker who successfully exploits this vulnerability can obtain sensitive information including but not limited to private SSH keys, session tokens, and other cryptographic material stored in the client's memory. This exposure directly undermines the fundamental security model of SSH connections, as private keys are critical components that, once compromised, allow attackers to impersonate legitimate users and gain unauthorized access to protected systems. The vulnerability is particularly dangerous in environments where users maintain multiple SSH connections or where the client operates in roaming configurations, as it provides an attack vector that can be exploited without requiring authentication to the target system. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1005 as "Data from Local System" and T1552 as "Unsecured Credentials," representing a sophisticated approach to credential harvesting.
The remediation for this vulnerability requires immediate patching of OpenSSH clients to versions 7.1p2 or later, where the resend_bytes function has been properly modified to validate buffer parameters and prevent excessive memory transmission. System administrators should also implement monitoring solutions to detect anomalous buffer transmission patterns that might indicate exploitation attempts. Security best practices recommend that organizations conduct comprehensive vulnerability assessments to identify affected systems and ensure all SSH clients are updated to patched versions. Additionally, organizations should consider implementing network segmentation and access controls to limit the potential impact of successful exploitation, while maintaining regular security updates to prevent similar vulnerabilities from arising in the future. The vulnerability demonstrates the importance of proper memory management in security-critical applications and highlights the necessity of thorough code review processes to identify and mitigate information disclosure risks in cryptographic software implementations.