CVE-2021-1223 in Integrated Services Router
Summary
by MITRE • 01/14/2021
Multiple Cisco products are affected by a vulnerability in the Snort detection engine that could allow an unauthenticated, remote attacker to bypass a configured file policy for HTTP. The vulnerability is due to incorrect handling of an HTTP range header. An attacker could exploit this vulnerability by sending crafted HTTP packets through an affected device. A successful exploit could allow the attacker to bypass configured file policy for HTTP packets and deliver a malicious payload.
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Analysis
by VulDB Data Team • 02/14/2021
The vulnerability identified as CVE-2021-1223 represents a critical security flaw within Cisco's Snort detection engine implementation across multiple network security appliances. This weakness specifically targets the handling of HTTP range headers within the file policy enforcement mechanisms, creating a significant bypass opportunity for malicious actors. The vulnerability affects Cisco products that utilize Snort as their core detection engine, including various firewalls, intrusion prevention systems, and network security appliances that rely on HTTP content filtering capabilities. The flaw stems from improper validation and processing of HTTP range header parameters that are commonly used in HTTP requests to retrieve partial content from web servers.
The technical exploitation of CVE-2021-1223 occurs through the manipulation of HTTP range headers in network traffic passing through affected Cisco devices. When an attacker crafts malicious HTTP packets containing specially formatted range headers, the Snort engine fails to properly evaluate these requests against configured file policies. This misconfiguration allows the detection engine to incorrectly process the HTTP traffic, effectively bypassing the intended security controls that should prevent certain file types from being transmitted or downloaded through the network. The vulnerability specifically impacts the HTTP file policy enforcement mechanism, which is designed to block or restrict the transfer of potentially malicious file types based on predefined rules and content filters.
The operational impact of this vulnerability extends beyond simple bypass of content filtering, as it enables attackers to deliver malicious payloads that would normally be blocked by security policies. An unauthenticated remote attacker can leverage this weakness to circumvent network security controls without requiring any credentials or privileged access to the affected devices. The exploitation process does not require specialized tools or deep technical knowledge of the underlying network infrastructure, making it particularly dangerous for organizations that rely on HTTP content filtering as a primary defense mechanism. This vulnerability essentially undermines the integrity of the security policy enforcement, allowing attackers to deliver malware, exploit code, or other malicious content that would typically be prevented by configured file restrictions.
Organizations affected by CVE-2021-1223 should prioritize immediate remediation through official Cisco security advisories and patches. The vulnerability aligns with CWE-20, which describes improper input validation, and represents a classic example of how malformed HTTP headers can be exploited to bypass security controls. From an ATT&CK framework perspective, this vulnerability maps to techniques involving proxy execution and command and control communications, as attackers can use the bypassed policies to establish covert channels or deliver payloads. Network administrators should implement additional monitoring and logging of HTTP traffic patterns, particularly around range header usage, to detect potential exploitation attempts. The remediation process requires careful planning to ensure that patch deployment does not disrupt existing network operations, while also implementing network segmentation to limit the potential impact if exploitation occurs. Organizations should also review their existing HTTP content filtering policies to identify any additional weaknesses that might compound the risk posed by this vulnerability.