CVE-2013-6479 in Pidgin
Summary
by MITRE
util.c in libpurple in Pidgin before 2.10.8 does not properly allocate memory for HTTP responses that are inconsistent with the Content-Length header, which allows remote HTTP servers to cause a denial of service (application crash) via a crafted response.
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Analysis
by VulDB Data Team • 06/08/2021
The vulnerability identified as CVE-2013-6479 affects the libpurple library component within Pidgin messaging software, specifically targeting memory allocation mechanisms during HTTP response processing. This flaw exists in versions prior to 2.10.8 and represents a classic buffer management issue that can be exploited to trigger application instability. The vulnerability stems from insufficient validation of HTTP response headers, particularly the Content-Length field, which creates a mismatch between expected and actual response sizes.
The technical implementation of this vulnerability resides in the util.c file where HTTP response handling occurs. When Pidgin receives an HTTP response from a remote server, it parses the Content-Length header to determine how much memory to allocate for the response data. However, the code fails to properly validate or handle cases where the actual response data differs significantly from the declared Content-Length value. This discrepancy creates a scenario where memory allocation either becomes insufficient or excessive, leading to memory corruption that ultimately results in application crash.
From an operational perspective, this vulnerability presents a significant denial of service risk to users of Pidgin messaging clients. Attackers can craft malicious HTTP responses that deliberately misalign the Content-Length header with actual response data, causing Pidgin to crash when attempting to process these responses. The impact extends beyond simple service interruption as it can affect communication reliability for users who depend on Pidgin for instant messaging and chat services. This vulnerability is particularly concerning in environments where Pidgin is used for business communications or as part of larger communication infrastructures.
The vulnerability aligns with CWE-122, which describes improper handling of memory allocation and deallocation, and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks. The flaw demonstrates poor input validation practices where the software fails to implement proper bounds checking on received HTTP responses. Security researchers have noted that such memory handling issues often stem from inadequate defensive programming practices that fail to account for malformed or malicious inputs. The vulnerability specifically relates to the HTTP protocol handling within the libpurple library, which forms the foundation for Pidgin's various network communication capabilities.
Mitigation strategies for this vulnerability include immediate upgrade to Pidgin version 2.10.8 or later, which contains the necessary patches to properly validate HTTP response headers. Organizations should implement network monitoring to detect unusual HTTP traffic patterns that might indicate exploitation attempts. Additionally, administrators should consider implementing proxy or firewall rules that can filter malformed HTTP responses before they reach vulnerable Pidgin instances. The fix implemented in the patched version addresses the core memory allocation issue by ensuring proper validation of Content-Length headers against actual response data, preventing the buffer overflow conditions that previously caused crashes.