CVE-2025-71263 in UNIX
Summary
by MITRE • 03/13/2026
In UNIX Fourth Research Edition (v4), the su command is vulnerable to a buffer overflow due to the 'password' variable having a fixed size of 100 bytes. A local user can exploit this to gain root privileges. It is unlikely that UNIX v4 is running anywhere outside of a very small number of lab environments. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.
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Analysis
by VulDB Data Team • 03/22/2026
The vulnerability identified as CVE-2025-71263 resides within the UNIX Fourth Research Edition (v4) operating system, specifically within the su command implementation. This represents a classic buffer overflow vulnerability that stems from inadequate input validation and fixed buffer sizing. The su command, designed to allow users to switch to the root account, contains a critical flaw in its password handling mechanism where the password variable is statically allocated with only 100 bytes of storage capacity. This fixed-size buffer presents a significant security risk as it fails to account for potential input lengths that may exceed this predetermined limit, creating an exploitable condition that can be leveraged by malicious actors.
The technical nature of this vulnerability aligns with CWE-121, which describes buffer overflow conditions where insufficient space is allocated for data storage, and more specifically with CWE-787, which addresses out-of-bounds write vulnerabilities. The flaw occurs during the password input processing phase of the su command, where user-provided credentials are stored in the fixed 100-byte buffer without proper bounds checking. When an attacker provides a password exceeding 100 characters, the excess data overflows into adjacent memory locations, potentially corrupting program execution flow and enabling arbitrary code execution. This type of vulnerability falls under the ATT&CK framework category of privilege escalation through T1068, which involves exploiting vulnerabilities to gain elevated privileges.
The operational impact of this vulnerability is severe despite the limited deployment of UNIX v4 in contemporary environments. A local attacker who successfully exploits this buffer overflow can achieve complete system compromise by gaining root privileges, effectively bypassing all user access controls and system security mechanisms. The vulnerability represents a critical escalation path that allows unauthorized users to assume administrative control over affected systems, potentially leading to data exfiltration, system modification, or complete service disruption. The attack vector requires local access to the system, making it less immediately dangerous than remote exploits, but still poses significant risk in environments where physical or logical access controls are insufficient.
Mitigation strategies for this vulnerability are largely constrained by the end-of-life status of UNIX v4 and its research-only deployment context. The most effective remediation involves immediate system decommissioning or replacement with modern, supported operating systems that implement proper input validation and memory management practices. Organizations maintaining legacy UNIX v4 systems should consider implementing additional access controls, network segmentation, and monitoring solutions to limit potential exploitation opportunities. The vulnerability demonstrates the critical importance of proper buffer management and input validation in system security, serving as a historical example of how insufficient memory safety measures can create persistent security weaknesses that remain exploitable even decades after initial implementation. Given the age of this system and the limited deployment scope, the primary recommendation remains the complete replacement or retirement of affected systems rather than attempting to patch the vulnerability directly.