CVE-2020-29019 in FortiWeb
Summary
by MITRE • 01/14/2021
A stack-based buffer overflow vulnerability in FortiWeb 6.3.0 through 6.3.7 and version before 6.2.4 may allow a remote, unauthenticated attacker to crash the httpd daemon thread by sending a request with a crafted cookie header.
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Analysis
by VulDB Data Team • 10/28/2024
This vulnerability represents a critical stack-based buffer overflow in FortiWeb web application firewalls affecting versions 6.3.0 through 6.3.7 and releases prior to 6.2.4. The flaw exists within the httpd daemon thread responsible for processing incoming HTTP requests, specifically when handling cookie headers. Attackers can exploit this weakness by crafting malicious cookie values that exceed the allocated stack buffer space, leading to memory corruption and subsequent daemon thread crashes. The vulnerability is particularly concerning because it requires no authentication credentials and can be triggered remotely, making it highly accessible to threat actors. This issue falls under CWE-121 Stack-based Buffer Overflow, which is classified as a fundamental memory safety vulnerability where data written to a stack buffer exceeds its allocated boundaries. The attack vector aligns with ATT&CK technique T1203, specifically targeting application layer vulnerabilities to disrupt service availability through denial of service mechanisms.
The technical exploitation of this vulnerability occurs when the httpd daemon processes HTTP requests containing oversized cookie headers that are not properly validated or sanitized before being copied into fixed-size stack buffers. When the cookie data exceeds the buffer capacity, it overflows into adjacent memory locations, potentially corrupting stack metadata, return addresses, or other critical program state information. This memory corruption typically results in immediate thread termination and daemon instability, causing service disruption for legitimate users. The vulnerability demonstrates poor input validation practices and inadequate bounds checking mechanisms within the FortiWeb application layer processing code. The impact extends beyond simple service disruption as the repeated exploitation can lead to complete daemon exhaustion and prolonged availability issues.
From an operational perspective, this vulnerability poses significant risk to organizations relying on FortiWeb for web application protection and security enforcement. The remote exploitation capability means attackers can target these devices from anywhere on the internet without requiring physical access or prior authentication, making it particularly dangerous for publicly exposed web application firewalls. The vulnerability affects the core functionality of the FortiWeb appliance, potentially leaving protected web applications exposed to direct attacks while the firewall itself is compromised. Organizations may experience extended downtime as the daemon crashes repeatedly, and the automatic restart mechanisms may not prevent service degradation or complete outages. This vulnerability directly impacts the availability and integrity of web application security services, creating potential attack vectors for more sophisticated exploitation attempts.
Organizations should implement immediate mitigation strategies including applying the latest firmware updates from Fortinet that address this specific buffer overflow vulnerability. Network segmentation and access controls should be enforced to limit exposure of FortiWeb appliances to untrusted networks and reduce attack surface. Implementing rate limiting and request validation mechanisms can help detect and prevent exploitation attempts before they cause daemon crashes. Monitoring systems should be configured to alert on unusual daemon behavior or frequent thread restarts that may indicate exploitation attempts. The vulnerability demonstrates the importance of regular security patching and vulnerability management processes, as this issue was resolved through official firmware updates. Additionally, organizations should consider implementing intrusion detection systems to monitor for suspicious cookie header patterns that may indicate exploitation attempts, and maintain robust backup and recovery procedures to minimize downtime during remediation activities.