CVE-2006-6169 in GnuPG
Summary
by MITRE
Heap-based buffer overflow in the ask_outfile_name function in openfile.c for GnuPG (gpg) 1.4 and 2.0, when running interactively, might allow attackers to execute arbitrary code via messages with "C-escape" expansions, which cause the make_printable_string function to return a longer string than expected while constructing a prompt.
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Analysis
by VulDB Data Team • 08/09/2019
The vulnerability identified as CVE-2006-6169 represents a critical heap-based buffer overflow in GnuPG's openfile.c component affecting versions 1.4 and 2.0. This flaw exists within the ask_outfile_name function where interactive GnuPG operations process messages containing C-escape expansions. The vulnerability stems from inadequate input validation and memory management when handling string expansions, creating a scenario where attacker-controlled data can cause memory corruption. The issue manifests when the make_printable_string function processes escape sequences, resulting in unexpectedly long output strings that exceed the allocated buffer boundaries. This type of vulnerability falls under CWE-121 Heap-based Buffer Overflow, which is classified as a memory safety issue where data written to heap memory exceeds the allocated bounds. The attack vector requires an interactive GnuPG session where users encounter messages containing specially crafted C-escape sequences, making this a user-interaction dependent exploit that aligns with ATT&CK technique T1059.007 for command and scripting interpreter execution.
The technical exploitation of this vulnerability occurs when GnuPG processes interactive prompts containing C-escape expansions such as \n, \t, or other escape sequences that when processed by make_printable_string function result in string lengths that surpass the originally allocated buffer space. The heap overflow occurs because the system does not properly account for the expansion of escape sequences during buffer allocation, leading to memory corruption that can be leveraged for arbitrary code execution. Attackers can craft malicious messages with escape sequences that, when processed by the vulnerable function, cause the buffer to overflow into adjacent memory locations. This memory corruption can overwrite critical program data, function pointers, or return addresses, enabling attackers to redirect program execution flow. The vulnerability's impact is particularly severe in interactive environments where users are prompted to confirm file operations, making it a prime target for social engineering attacks that combine user interaction with code execution capabilities.
The operational impact of CVE-2006-6169 extends beyond simple privilege escalation to include complete system compromise when attackers successfully exploit the buffer overflow. In practical scenarios, this vulnerability could be exploited in email clients or file management systems that utilize GnuPG for encryption operations, allowing attackers to execute malicious code with the privileges of the GnuPG process. The vulnerability affects both GnuPG 1.4 and 2.0 versions, indicating a long-standing issue that persisted across major releases. The exploitation requires minimal privileges since the vulnerability exists within the interactive prompt processing functionality, making it particularly dangerous in environments where users regularly interact with GnuPG for encryption and decryption tasks. Organizations using GnuPG for secure communications, digital signatures, or email encryption face significant risk exposure, as the vulnerability can be triggered through legitimate user interactions with encrypted messages or files.
Mitigation strategies for this vulnerability require immediate patching of affected GnuPG versions to address the heap overflow in the make_printable_string function. System administrators should ensure all GnuPG installations are updated to versions that properly validate string expansion lengths and implement proper buffer boundary checks. Input sanitization measures should be implemented to filter or escape C-escape sequences before they reach the vulnerable processing functions. Network segmentation and privilege separation can help limit the potential impact if exploitation occurs, ensuring that GnuPG processes run with minimal required privileges. Security monitoring should include detection of unusual string processing patterns or buffer-related system calls that might indicate exploitation attempts. Additionally, organizations should implement proper application whitelisting to restrict execution of untrusted GnuPG operations and consider using alternative encryption tools with more robust memory management practices. The vulnerability demonstrates the importance of proper memory management in cryptographic software and the critical need for thorough input validation in interactive applications, particularly those handling user-provided data that may contain escape sequences or special characters that could be exploited for memory corruption attacks.