CVE-2022-28652 in Apport (Billion Laughs)
Summary
by MITRE • 06/05/2024
~/.config/apport/settings parsing is vulnerable to "billion laughs" attack
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 05/15/2026
The vulnerability in ~/.config/apport/settings parsing represents a critical security flaw that enables denial of service through resource exhaustion attacks. This issue affects the apport crash reporting system used in ubuntu and debian based distributions where the system parses configuration files to determine crash reporting behavior. The vulnerability stems from improper input validation during the parsing of the settings file which allows maliciously crafted input to trigger exponential resource consumption patterns. When the parser encounters specially constructed data that appears benign but contains recursive references or repeated patterns, it can process these inputs in a manner that exponentially increases memory and cpu usage. This parsing behavior creates a perfect environment for what is commonly known as the "billion laughs" attack pattern where seemingly innocuous data structures can cause systems to consume massive amounts of computational resources. The vulnerability is particularly dangerous because it operates at the configuration parsing level, meaning that any process attempting to read or modify these settings could be affected, including system services that automatically parse configuration files during startup or operation. The attack can be executed by placing malicious content in the user configuration directory which is typically writable by regular users, making exploitation straightforward and potentially affecting system availability for all users.
The technical implementation of this vulnerability exposes a fundamental flaw in the XML or configuration parsing logic that fails to implement proper recursion depth limits or resource consumption checks. The parser likely uses a recursive descent approach or similar parsing technique that does not enforce bounds on nested structures or repeated pattern expansion. This design flaw allows an attacker to craft input that appears legitimate but contains patterns that cause the parser to expand data structures exponentially, leading to memory exhaustion and system instability. The vulnerability is classified as a resource exhaustion issue that can be categorized under common weakness enumeration CWE-400 which specifically addresses "Uncontrolled Resource Consumption" in software systems. The attack vector is particularly concerning because it requires minimal privileges and can be executed through modification of user configuration files, making it an attractive target for attackers seeking to disrupt system availability. The configuration file parsing mechanism is often used during system boot processes and service initialization, meaning that exploitation can cause cascading failures throughout the system. The attack follows patterns consistent with the attack technique T1499.004 from the attack tactic T1499 which covers "Resource Hijacking" and specifically targets the consumption of system resources to cause denial of service conditions.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise system integrity and availability across multiple user sessions. When exploited, the vulnerability can cause system services to become unresponsive, applications to crash, or in severe cases, entire system shutdowns due to resource exhaustion. The attack is particularly effective in server environments where multiple users might be running applications that rely on configuration parsing, creating a potential for widespread service disruption. The vulnerability affects both desktop and server installations of affected distributions, making it relevant across different deployment scenarios. System administrators may not immediately recognize the cause of performance degradation or service outages since the attack operates through legitimate configuration file parsing mechanisms. The attack can also be combined with other techniques to create more sophisticated denial of service scenarios, particularly when targeting specific services that rely on the affected configuration parsing functionality. Monitoring systems may not detect this attack as it appears to be normal system behavior, making detection and response more challenging. The vulnerability's impact is amplified in environments where automated processes continuously parse configuration files, as these processes can be targeted to create sustained resource exhaustion conditions.
Mitigation strategies for this vulnerability require both immediate patching and architectural improvements to prevent similar issues in the future. The primary solution involves updating the affected apport package to a version that implements proper recursion depth limits and resource consumption checks during configuration file parsing. System administrators should ensure that all affected systems are updated immediately, particularly in production environments where availability is critical. Additional protective measures include implementing file access controls to restrict modification of configuration directories, monitoring for unusual resource consumption patterns, and implementing automated detection systems that can identify potentially malicious configuration file content. The configuration parsing logic should be reviewed to implement proper input validation that prevents recursive structures from causing exponential expansion, which aligns with the defensive programming principles outlined in secure coding standards. Organizations should also consider implementing configuration management policies that limit the ability of end users to modify system configuration files, particularly those used by critical system services. Network monitoring solutions should be configured to detect unusual parsing behavior or resource consumption spikes that could indicate exploitation attempts. Long-term remediation efforts should include code reviews focused on parsing logic to ensure that all configuration file parsers implement appropriate safeguards against resource exhaustion attacks, following the security guidelines established in both CWE and NIST cybersecurity frameworks to prevent similar vulnerabilities from emerging in future implementations.