CVE-2015-5309 in PuTTY
Summary
by MITRE
Integer overflow in the terminal emulator in PuTTY before 0.66 allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code via an ECH (erase characters) escape sequence with a large parameter value, which triggers a buffer underflow.
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Analysis
by VulDB Data Team • 11/23/2024
The vulnerability identified as CVE-2015-5309 represents a critical integer overflow flaw within the terminal emulator component of PuTTY versions prior to 0.66. This issue stems from inadequate input validation when processing escape sequences, specifically the ECH (erase characters) command, which is part of the standard terminal control protocols used for managing text display in terminal emulators. The vulnerability operates at the intersection of software security and terminal emulation protocols, where malicious actors can exploit malformed escape sequences to manipulate memory structures within the application.
The technical implementation of this vulnerability involves an integer overflow condition that occurs when processing the ECH escape sequence with an excessively large parameter value. When PuTTY receives such a sequence, the application fails to properly validate the parameter size, leading to an integer overflow that subsequently causes a buffer underflow condition. This memory corruption scenario creates opportunities for remote attackers to either induce a denial of service through application crashes or potentially achieve arbitrary code execution within the context of the running PuTTY process. The underlying flaw aligns with CWE-190, which specifically addresses integer overflow conditions, and CWE-121, which deals with stack-based buffer overflow vulnerabilities.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential remote code execution capabilities that could allow attackers to compromise systems using PuTTY as a terminal client. Attackers could leverage this vulnerability by establishing a connection to a target system and sending specially crafted escape sequences through SSH or Telnet connections, effectively exploiting the terminal emulator's parsing logic. The vulnerability affects systems where PuTTY is used as a terminal client for remote access, making it particularly dangerous in enterprise environments where SSH connections are frequently established. This flaw demonstrates how terminal emulators can become attack vectors when they fail to properly sanitize escape sequence parameters, creating a pathway for privilege escalation or system compromise.
Mitigation strategies for CVE-2015-5309 primarily focus on immediate patching of affected PuTTY versions to 0.66 or later, which includes proper integer overflow checks and enhanced input validation for escape sequences. Organizations should implement network segmentation and access controls to limit exposure to potentially malicious connections, while also monitoring for unusual terminal behavior or connection patterns that might indicate exploitation attempts. Security teams should consider implementing network-based intrusion detection systems that can identify and block malformed escape sequences, particularly those with suspicious parameter values. The vulnerability also highlights the importance of adhering to secure coding practices, specifically regarding integer arithmetic validation and buffer management, which aligns with ATT&CK technique T1059.005 for command and scripting interpreter usage. Additionally, system administrators should conduct regular security assessments of terminal emulators and remote access tools to identify similar vulnerabilities that might exist in other components of their infrastructure, ensuring comprehensive protection against similar memory corruption attacks.