CVE-2009-3084 in Pidgin
Summary
by MITRE
The msn_slp_process_msg function in libpurple/protocols/msn/slpcall.c in the MSN protocol plugin in libpurple 2.6.0 and 2.6.1, as used in Pidgin before 2.6.2, allows remote attackers to cause a denial of service (application crash) via a handwritten (aka Ink) message, related to an uninitialized variable and the incorrect "UTF16-LE" charset name.
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Analysis
by VulDB Data Team • 08/22/2021
The vulnerability identified as CVE-2009-3084 represents a critical denial of service flaw within the MSN protocol implementation of libpurple, the core messaging library used by Pidgin and other instant messaging clients. This issue specifically affects versions 2.6.0 and 2.6.1 of libpurple, which were widely deployed in various instant messaging applications. The vulnerability manifests through the msn_slp_process_msg function located in the file libpurple/protocols/msn/slpcall.c, which handles the processing of Session Location Protocol messages within the MSN messaging system. The flaw occurs when the application receives a specially crafted handwritten (Ink) message from a remote attacker, causing the targeted application to crash and become unavailable to legitimate users.
The technical root cause of this vulnerability stems from improper handling of character encoding within the message processing pipeline. The msn_slp_process_msg function contains an uninitialized variable that is subsequently used in the context of UTF16-LE character set processing. This uninitialized variable, when combined with the incorrect "UTF16-LE" charset name specification, creates a condition where memory access violations can occur during message parsing. The flaw exemplifies a classic uninitialized variable vulnerability, which maps to CWE-457 in the Common Weakness Enumeration catalog, specifically addressing the use of uninitialized variables in security-critical contexts. The improper character encoding handling demonstrates weaknesses in input validation and data processing that can lead to unpredictable application behavior and system instability.
The operational impact of this vulnerability extends beyond simple application crashes to potentially disrupt communication services for users relying on MSN protocol support within Pidgin and similar applications. Attackers can exploit this weakness by crafting malicious Ink messages that trigger the uninitialized variable access, causing the application to terminate unexpectedly and forcing users to restart their messaging clients. This type of denial of service attack can be particularly disruptive in environments where instant messaging serves as a primary communication channel, as it can effectively cut off user access to messaging services until the application is manually restarted. The vulnerability affects not just individual users but can potentially impact larger communication infrastructures where multiple users depend on the same messaging platform.
The remediation for this vulnerability required the development of proper input validation mechanisms and the initialization of all variables before use within the message processing function. The fix implemented in Pidgin version 2.6.2 addressed the uninitialized variable issue by ensuring that all memory locations are properly initialized before processing UTF16-LE encoded messages. This update aligns with security best practices outlined in the ATT&CK framework under the T1499 category, specifically addressing the exploitation of memory corruption vulnerabilities. Organizations using affected versions of libpurple should prioritize immediate patching to prevent exploitation, as the vulnerability does not require authentication or special privileges to trigger, making it particularly dangerous in uncontrolled network environments where users may receive unsolicited messages from external sources.