CVE-2006-5556 in HP-UX
Summary
by MITRE
Buffer overflow in the localtime_r function, and certain other functions, in libc in HP-UX B.11.11 and possibly other versions allows local users to execute arbitrary code via a long TZ environment variable.
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Analysis
by VulDB Data Team • 04/25/2026
The vulnerability described in CVE-2006-5556 represents a critical buffer overflow condition within the libc library of HP-UX operating systems, specifically affecting version B.11.11 and potentially other iterations. This flaw exists within the localtime_r function and related time manipulation routines that process environment variables, creating an exploitable condition that can be leveraged by local attackers to gain unauthorized code execution privileges. The issue stems from insufficient bounds checking when handling the TZ environment variable, which is used to specify time zone information for system operations. When a maliciously crafted long TZ variable is provided, the buffer overflow occurs during the processing of time zone data, allowing attackers to overwrite adjacent memory locations and potentially execute arbitrary code with the privileges of the affected process.
The technical implementation of this vulnerability involves the improper handling of environment variable data within the libc library functions, particularly those responsible for time zone processing and conversion. The localtime_r function, which is designed to convert time values to local time representation in a thread-safe manner, fails to validate the length of the TZ environment variable before copying it into fixed-size buffers. This design flaw creates a classic buffer overflow scenario where the amount of data written exceeds the allocated buffer space, leading to memory corruption that can be exploited to redirect program execution flow. The vulnerability specifically targets the stack-based buffer overflow pattern, where the overflow occurs in the automatic storage area of functions, potentially allowing attackers to overwrite return addresses, function pointers, or other critical control data structures.
From an operational perspective, this vulnerability poses significant risks to HP-UX systems running affected versions, as local users can exploit the condition to execute arbitrary code without requiring remote network access. The attack vector requires local system access, making it a local privilege escalation vulnerability that can be particularly dangerous in multi-user environments where users may have varying privilege levels. Successful exploitation could result in complete system compromise, allowing attackers to gain elevated privileges, install backdoors, or establish persistent access to the affected systems. The impact extends beyond individual system compromise, as compromised systems can serve as launch points for further attacks within network environments, potentially leading to widespread security breaches. This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a common attack pattern that has been extensively documented in security literature.
The mitigation strategies for CVE-2006-5556 focus on both immediate remediation and long-term security hardening measures. The primary recommendation involves applying the vendor-provided patches or updates that address the buffer overflow in the libc library functions. System administrators should also implement environment variable validation and sanitization procedures to prevent overly long or malformed TZ values from being processed by system applications. Additional protective measures include implementing proper access controls to limit local user privileges, monitoring for unusual environment variable usage patterns, and employing runtime protection mechanisms such as stack canaries or address space layout randomization. Organizations should also consider implementing security awareness training for system administrators to recognize potential exploitation attempts and maintain updated vulnerability management processes that include regular system patching and security assessments. This vulnerability demonstrates the importance of proper input validation and memory safety practices in system libraries, as highlighted by ATT&CK technique T1068 which covers local privilege escalation through exploitation of system vulnerabilities.