CVE-2015-8708 in Claws Mail
Summary
by MITRE
Stack-based buffer overflow in the conv_euctojis function in codeconv.c in Claws Mail 3.13.1 allows remote attackers to have unspecified impact via a crafted email, involving Japanese character set conversion. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-8614.
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Analysis
by VulDB Data Team • 11/08/2024
The vulnerability identified as CVE-2015-8708 represents a stack-based buffer overflow within the Claws Mail email client version 3.13.1, specifically within the conv_euctojis function located in the codeconv.c source file. This flaw manifests during the processing of email messages containing Japanese character set encoding, particularly when the application attempts to convert between different character encodings. The vulnerability stems from an incomplete remediation of a previously addressed issue, CVE-2015-8614, which demonstrates a pattern of insufficient security fixes that leave applications vulnerable to exploitation. The buffer overflow occurs when the application processes malformed or specially crafted email content that triggers the character set conversion routine, creating a condition where data written to a stack buffer exceeds its allocated bounds.
The technical implementation of this vulnerability involves the conv_euctojis function which handles the conversion of EUC-JP (Extended Unix Code for Japanese) character encodings to other formats. When processing email messages containing specially crafted Japanese character sequences, the function fails to properly validate input lengths before copying data into fixed-size stack buffers. This inadequate bounds checking allows attackers to overwrite adjacent stack memory locations, potentially leading to arbitrary code execution or application crashes. The vulnerability is particularly concerning because it operates during normal email processing operations, making it difficult to detect and exploit through standard security monitoring approaches. The flaw aligns with CWE-121 Stack-based Buffer Overflow, which describes buffer overflow conditions where insufficient bounds checking allows data to overwrite adjacent memory locations on the stack.
From an operational perspective, this vulnerability presents significant risks to email server and client security as it enables remote code execution through the delivery of maliciously crafted emails. Attackers can exploit this weakness by sending specially formatted messages containing Japanese character sequences that trigger the vulnerable conversion function, potentially allowing them to execute arbitrary code with the privileges of the affected user or system. The impact extends beyond individual user compromise to potential system-wide exploitation, especially in environments where email servers process untrusted content from external sources. The vulnerability's remote exploitability means that attackers do not need physical access to target systems, making it particularly dangerous in enterprise environments where email communication is frequent and automated. This aligns with ATT&CK technique T1190 for Exploit Public-Facing Application and T1059 for Command and Scripting Interpreter, as the vulnerability enables attackers to execute malicious code through email-based delivery mechanisms.
The remediation approach for CVE-2015-8708 requires immediate patching of Claws Mail to version 3.13.2 or later, which contains a complete fix for both CVE-2015-8614 and CVE-2015-8708. Organizations should implement comprehensive email filtering solutions that can detect and quarantine suspicious character encoding patterns before they reach end-user systems. Network administrators should consider implementing email security gateways that can identify and block malformed character sequences in email attachments and content. Security teams should also conduct regular vulnerability assessments to identify similar incomplete fixes in other applications and libraries. The fix addresses the root cause by implementing proper bounds checking in the conv_euctojis function and ensuring that all character conversion operations validate input sizes against allocated buffer capacities. Additionally, organizations should consider deploying application whitelisting solutions and privilege separation mechanisms to limit the potential impact of successful exploitation attempts, as the vulnerability could enable attackers to escalate privileges or gain persistent access to compromised systems.