CVE-2016-0778 in Mac OS X
Summary
by MITRE
The (1) roaming_read and (2) roaming_write functions in roaming_common.c in the client in OpenSSH 5.x, 6.x, and 7.x before 7.1p2, when certain proxy and forward options are enabled, do not properly maintain connection file descriptors, which allows remote servers to cause a denial of service (heap-based buffer overflow) or possibly have unspecified other impact by requesting many forwardings.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability described in CVE-2016-0778 represents a critical heap-based buffer overflow in OpenSSH client implementations affecting versions 5.x through 7.x before 7.1p2. This flaw specifically resides in the roaming_common.c file within the client-side codebase and manifests when certain proxy and forwarding options are enabled during SSH connections. The issue stems from improper handling of connection file descriptors during the roaming_read and roaming_write function operations, creating a pathway for remote attackers to exploit the system through carefully crafted forwarding requests.
The technical implementation of this vulnerability involves the improper management of file descriptor states within the SSH client's roaming functionality. When proxy and forwarding options are active, the client's roaming_read and roaming_write functions fail to correctly maintain the state of connection file descriptors, leading to memory corruption issues. The heap-based buffer overflow occurs because the functions do not properly validate or limit the number of forwardings that can be requested, allowing attackers to repeatedly trigger forwarding operations that eventually exhaust memory resources or corrupt heap structures. This vulnerability operates at the protocol level within SSH client implementations and can be exploited through malicious SSH servers that initiate excessive forwarding requests.
The operational impact of CVE-2016-0778 extends beyond simple denial of service to potentially enable more severe consequences including arbitrary code execution or system compromise. The vulnerability affects the stability of SSH client applications and can be leveraged by attackers to disrupt legitimate SSH connections, making it particularly dangerous in environments where SSH clients are frequently used for remote access and system administration. The memory corruption issues can lead to unpredictable behavior in the client application, potentially allowing attackers to execute malicious code or gain elevated privileges depending on the specific implementation and system configuration. This vulnerability is especially concerning because it affects widely deployed SSH client software across multiple versions and can be exploited remotely without requiring authentication to the target system.
Mitigation strategies for this vulnerability include applying the official patch released with OpenSSH 7.1p2, which properly addresses the file descriptor management issues in the roaming functions. System administrators should immediately upgrade to patched versions of OpenSSH to eliminate the risk of exploitation. Additionally, organizations can implement network-level controls such as restricting access to SSH servers that might be compromised, monitoring for unusual forwarding patterns, and disabling proxy and forwarding options when they are not required for specific use cases. The vulnerability aligns with CWE-121, heap-based buffer overflow, and maps to ATT&CK technique T1021.004 for remote service manipulation. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of exploitation, as well as conducting regular security assessments to identify other potential vulnerabilities in SSH implementations.