CVE-2022-22707 in lighttpd
Summary
by MITRE • 01/06/2022
In lighttpd 1.4.46 through 1.4.63, the mod_extforward_Forwarded function of the mod_extforward plugin has a stack-based buffer overflow (4 bytes), as demonstrated by remote denial of service (daemon crash).
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Analysis
by VulDB Data Team • 01/09/2022
The vulnerability identified as CVE-2022-22707 affects the lighttpd web server software version 1.4.46 through 1.4.63, specifically within the mod_extforward plugin module. This issue represents a critical stack-based buffer overflow condition that can be exploited remotely to cause daemon crashes and subsequent denial of service. The vulnerability resides in the mod_extforward_Forwarded function which processes forwarded headers in HTTP requests. When an attacker crafts a malicious HTTP request containing specially formatted forwarded headers, the function fails to properly validate input length before copying data to a fixed-size stack buffer. This flaw allows an attacker to overwrite adjacent stack memory locations with 4 bytes of data beyond the allocated buffer boundaries, potentially leading to unpredictable behavior including program termination and service disruption. The vulnerability is particularly concerning because it operates at the protocol level where HTTP headers are processed, making it accessible through standard web traffic without requiring authentication or special privileges.
The technical implementation of this vulnerability stems from improper bounds checking within the mod_extforward plugin's Forwarded header processing logic. CWE-121 defines this as a classic stack-based buffer overflow where insufficient input validation allows data to overflow into adjacent memory locations. The attack vector is remote and can be executed by sending malformed HTTP requests containing excessive forwarded header data to a vulnerable lighttpd instance. The specific 4-byte overflow indicates that the buffer size allocated for header processing is insufficient to handle the length of data being copied, creating a predictable memory corruption scenario. The vulnerability's impact is primarily focused on availability rather than confidentiality or integrity, as it specifically enables denial of service conditions that cause the web server daemon to crash and restart. However, the memory corruption aspect could potentially be exploited further in more complex attack scenarios, though the current disclosure focuses on the crash behavior.
The operational impact of CVE-2022-22707 extends beyond simple service disruption to potentially affect business continuity and system availability for organizations relying on lighttpd as their web server solution. Any web application or service that utilizes lighttpd with the mod_extforward plugin becomes vulnerable to this attack, particularly those that process forwarded headers from load balancers, proxies, or client applications. The vulnerability affects the entire range of lighttpd versions from 1.4.46 through 1.4.63, representing a substantial attack surface across multiple releases. Organizations using lighttpd in production environments face significant risk of service interruption, especially during peak traffic periods when the server is most vulnerable to exploitation. The remote nature of the attack means that adversaries can target vulnerable systems from anywhere on the internet without requiring physical access or prior authentication, making this vulnerability particularly dangerous for publicly exposed web servers. This vulnerability directly maps to ATT&CK technique T1499.004 which covers network denial of service attacks, and T1595.001 which involves reconnaissance of target network infrastructure to identify vulnerable services.
Mitigation strategies for CVE-2022-22707 primarily involve immediate software updates to versions that have patched the buffer overflow vulnerability. System administrators should upgrade to lighttpd version 1.4.64 or later where the mod_extforward plugin has been fixed to properly validate input lengths before buffer operations. Organizations should also implement network-level protections including firewall rules that restrict access to forwarded header processing endpoints and monitoring systems that can detect abnormal HTTP request patterns. The mod_extforward plugin itself should be disabled if it is not actively required for the web server's operation, as this eliminates the attack surface entirely. Additionally, organizations can implement request size limits and header validation mechanisms at the network level to prevent overly long header values from reaching the vulnerable code path. Regular security assessments and vulnerability scanning should be conducted to identify other potential vulnerabilities in the web server configuration. The fix implemented by the lighttpd development team addresses the root cause by introducing proper bounds checking and input validation in the Forwarded header processing function, preventing the buffer overflow condition from occurring while maintaining the intended functionality of the plugin.