Critical Buffer Overflow Vulnerability Discovered in zlib’s untgz Utility
A significant security vulnerability has been identified in version 1.3.1.2 of the zlib untgz utility, a widely used tool for decompressing .tgz files. This flaw allows attackers to exploit a buffer overflow by providing specially crafted command-line inputs, potentially leading to memory corruption and the execution of arbitrary code.
Technical Details
The vulnerability resides in the `TGZfname()` function of the untgz utility. Specifically, the function employs an unbounded `strcpy()` call to process user-supplied archive names without validating their length. This oversight results in the copying of attacker-controlled input from the command line into a fixed-size static global buffer of 1,024 bytes, without any bounds checking.
This buffer overflow occurs immediately upon function entry, prior to any archive parsing or validation, making the vulnerability easily exploitable through command-line arguments alone.
Vulnerability Attributes
– CVE ID: Not yet assigned
– Affected Software: zlib untgz utility
– Affected Version: v1.3.1.2
– Vulnerability Type: Global Buffer Overflow
– CWE Classification: CWE-120 (Buffer Copy without Checking Size of Input)
– Attack Vector: Command-line input
– Potential Impact: Denial of Service, Memory Corruption, Potential Code Execution
Potential Impact
Security researchers have demonstrated that supplying an archive name exceeding 1,024 bytes triggers an out-of-bounds write past the buffer’s end, leading to memory corruption. The potential impacts include denial-of-service crashes, corruption of adjacent global memory objects, and undefined behavior.
More critically, depending on compiler settings, system architecture, build flags, and memory layout, attackers may be able to execute arbitrary code.
Researchers successfully triggered the vulnerability using AddressSanitizer (ASAN) by invoking untgz with a 4,096-byte filename argument. The ASAN output confirmed a global buffer overflow caused by a write of 2,001 bytes to the vulnerable memory address.
Because the overflow affects global memory rather than stack memory, the corruption persists beyond the function scope and can influence subsequent program behavior.
The vulnerability requires no special privileges and has low attack complexity, making it particularly dangerous for systems using the affected zlib untgz utility.
Mitigation Recommendations
To mitigate the risks associated with this vulnerability, users and administrators are advised to:
1. Update the zlib untgz Utility: Check for and apply any available patches or updates that address this vulnerability.
2. Implement Input Validation: Ensure that all user inputs, especially those from command-line arguments, are properly validated and sanitized to prevent buffer overflow exploits.
3. Use Secure Coding Practices: Replace unsafe functions like `strcpy()` with safer alternatives that include bounds checking, such as `strncpy()` or `strlcpy()`.
4. Conduct Regular Security Audits: Regularly review and test code for vulnerabilities, particularly in functions that handle user input or manipulate memory directly.
5. Monitor Systems for Unusual Activity: Implement monitoring to detect and respond to potential exploitation attempts promptly.
Conclusion
The discovery of this buffer overflow vulnerability in the zlib untgz utility underscores the importance of rigorous input validation and secure coding practices. By taking proactive measures to address this issue, organizations can protect their systems from potential exploitation and maintain the integrity and security of their data.
