CVE-2013-1864 in Portable Tool Library
Summary
by MITRE
The Portable Tool Library (aka PTLib) before 2.10.10, as used in Ekiga before 4.0.1, does not properly detect recursion during entity expansion, which allows remote attackers to cause a denial of service (memory and CPU consumption) via a crafted PXML document containing a large number of nested entity references, aka a "billion laughs attack."
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Analysis
by VulDB Data Team • 12/27/2024
The vulnerability identified as CVE-2013-1864 represents a critical denial of service weakness within the Portable Tool Library (PTLib) version 2.10.10 and earlier, which was utilized by Ekiga version 4.0.1 and earlier. This flaw specifically affects the XML parsing capabilities of these applications, creating a scenario where malicious actors can exploit recursive entity expansion to consume excessive system resources. The vulnerability stems from the library's inability to properly detect and limit recursive entity references during the parsing of PXML documents, which are commonly used in telephony and multimedia applications. The flaw is particularly dangerous because it can be triggered through seemingly innocuous XML documents that contain deeply nested entity references, making it difficult to detect during normal operation.
The technical implementation of this vulnerability aligns with the well-documented CWE-400 weakness category, which specifically addresses "Uncontrolled Resource Consumption" or "Denial of Service." This vulnerability operates under the principles of the "billion laughs attack" technique, a well-known method of exploiting XML parsers by creating massive amounts of data through recursive entity expansion. When a vulnerable application processes a crafted PXML document containing numerous nested entity references, each reference can expand into multiple copies of itself, leading to exponential growth in memory and CPU consumption. The attack works by creating entities that reference other entities, which in turn reference additional entities, creating a cascade effect that can quickly exhaust system resources. This mechanism is particularly effective against XML parsers that do not implement proper recursion limits or entity expansion depth checking.
The operational impact of CVE-2013-1864 extends beyond simple service disruption, as it can effectively render applications unusable for legitimate users while consuming significant system resources. In environments where Ekiga or applications built on PTLib are used for critical communications, this vulnerability could be exploited to create service interruptions that affect business operations or personal communications. The memory consumption grows exponentially with each level of nesting, making it possible for an attacker to consume gigabytes of RAM and CPU cycles from a relatively small malicious document. This type of attack is particularly challenging to defend against because it can be delivered through legitimate communication channels, such as incoming calls or file transfers, and the malicious content appears harmless until processed by the vulnerable application. The attack can be executed remotely without requiring authentication or special privileges, making it accessible to a wide range of potential attackers.
Mitigation strategies for this vulnerability focus on both immediate patching and architectural improvements to prevent similar issues. The most effective immediate solution is upgrading to PTLib version 2.10.10 or later, which includes proper recursion detection and limits on entity expansion. System administrators should also implement XML parser configuration settings that limit the depth of entity expansion and the number of entity references allowed in a single document. Additionally, network-level filtering can be implemented to detect and block suspicious XML content, particularly in environments where such content might be processed from untrusted sources. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for "Trusted Relationship" and T1059.007 for "Command and Scripting Interpreter" in the context of privilege escalation through application exploitation. Organizations should also consider implementing application whitelisting policies that restrict the execution of vulnerable applications until proper patches are deployed, and conduct regular vulnerability assessments to identify other potential XML parsing vulnerabilities in their software inventory.