CVE-2026-76663 in NonStop TELSERV
Summary
by MITRE • 10/15/2026
A stack-based buffer overflow vulnerability in HPE NonStop TELSERV can cause memory corruption that may result in DoS.
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Analysis
by VulDB Data Team • 10/15/2026
The HighPoint Enterprise (HPE) NonStop operating system, specifically within the TELSERV component which handles terminal server services and remote access connections, contains a critical stack-based buffer overflow vulnerability. This flaw arises from insufficient boundary checking when processing input data destined for internal buffers used by the telnet service daemon. The architecture of HPE NonStop relies heavily on high availability and continuous operation, making any disruption to core communication services particularly severe. When an attacker sends specially crafted packets containing oversized or malformed payload data to the TELSERV process, the application fails to validate the length of the input against the allocated stack space. This lack of validation allows the excess data to overwrite adjacent memory locations on the call stack, corrupting critical control structures such as return addresses and saved frame pointers.
From a technical perspective, this vulnerability is classified under CWE-121, which denotes a stack-based buffer overflow. The exploitation mechanism typically involves overwriting the instruction pointer or other control flow variables stored on the stack during function execution. While immediate exploitation for arbitrary code execution may be complex due to modern mitigations like non-executable stacks and address space layout randomization present in newer versions of NonStop, the primary confirmed impact is a denial of service condition. The memory corruption causes the TELSERV process to crash or become unresponsive, effectively severing remote terminal connections managed by that specific instance. In an environment where system uptime is paramount, such crashes can trigger automatic restarts or require manual intervention, leading to significant operational downtime and potential data loss if active sessions are abruptly terminated without proper state preservation mechanisms.
The operational impact extends beyond simple service interruption. TELSERV often serves as a gateway for administrative access to critical mainframe resources. A successful exploitation resulting in a denial of service could block administrators from accessing the system during maintenance windows or emergency recovery scenarios, thereby compounding the severity of any concurrent issues. Furthermore, if the vulnerability allows for more sophisticated attacks beyond simple crashing, it could potentially lead to privilege escalation or remote code execution, although current reports emphasize the stability and availability impact. The attack vector is generally network-based, requiring an attacker to have connectivity to the port serviced by TELSERV, typically TCP port 23 or a designated alternative telnet port. This makes the vulnerability accessible to any entity with network reachability to the affected host, whether from internal networks or potentially external sources if not properly segmented by firewalls.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. The primary defense is applying the vendor-provided software patches that address the input validation logic within TELSERV. Organizations should prioritize updating to versions where this buffer overflow has been rectified with proper length checks and safe string handling functions. In addition to patching, network segmentation plays a crucial role in limiting exposure. TELSERV services should be restricted to trusted management networks using access control lists or firewalls that block unauthorized external traffic from reaching the telnet ports. Given the sensitivity of remote administration tools, it is also advisable to migrate away from legacy protocols like Telnet toward more secure alternatives such as SSH, which provide encryption and stronger authentication mechanisms, thereby reducing the attack surface for protocol-specific vulnerabilities.
This vulnerability aligns with MITRE ATT&CK technique T1498, Network Denial of Service, specifically regarding resource exhaustion through service disruption. It also relates to CWE-20 Improper Input Validation, as the root cause is the failure to sanitize and verify incoming data before processing. Security teams should monitor logs for unusual patterns in TELSERV connections or unexpected process restarts that might indicate attempted exploitation activities. Regular vulnerability assessments targeting legacy services on mainframe environments are essential to identify such weaknesses before they can be leveraged by malicious actors. By combining timely patching with strict network access controls and protocol modernization, organizations can effectively neutralize the risk posed by this stack-based buffer overflow in HPE NonStop TELSERV.