CVE-2005-0039 in IPsec
Summary
by MITRE
Certain configurations of IPsec, when using Encapsulating Security Payload (ESP) in tunnel mode, integrity protection at a higher layer, or Authentication Header (AH), allow remote attackers to decrypt IPSec communications by modifying the outer packet in ways that cause plaintext data from the inner packet to be returned in ICMP messages, as demonstrated using bit-flipping attacks and (1) Destination Address Rewriting, (2) a modified header length that causes portions of the packet to be interpreted as IP Options, or (3) a modified protocol field and source address.
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Analysis
by VulDB Data Team • 02/03/2025
This vulnerability resides in the fundamental security mechanisms of ipsec implementations, specifically affecting the encapsulating security payload esp in tunnel mode configurations. The flaw represents a critical weakness in the cryptographic integrity protection that ipsec is designed to provide, allowing remote attackers to exploit specific packet manipulation techniques to recover plaintext data from encrypted communications. The vulnerability operates through a sophisticated attack vector that leverages the interaction between ipsec packet processing and icmp error message generation, creating a pathway for information disclosure that bypasses expected security boundaries.
The technical execution of this vulnerability involves three primary attack methods that exploit different aspects of ipsec packet handling and network protocol interpretation. The first method utilizes destination address rewriting to manipulate how the outer ip header is processed, causing the system to return portions of the inner packet data in icmp error messages. The second approach involves modifying the ip header length field to cause portions of the packet to be misinterpreted as ip options, which then get included in icmp responses. The third technique manipulates the protocol field and source address to achieve similar results through different packet parsing pathways. These attacks demonstrate how improper input validation and insufficient packet boundary checking can create security vulnerabilities even within well-established cryptographic protocols.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally undermines the confidentiality assurances that ipsec is designed to provide. Attackers can systematically recover plaintext data from encrypted communications by exploiting the specific packet modification techniques, potentially gaining access to sensitive information that was intended to remain protected. The vulnerability affects implementations that use esp in tunnel mode, ah authentication headers, or configurations that provide integrity protection at higher layers, making it particularly concerning for network security infrastructure. This weakness allows attackers to perform bit-flipping attacks that can be systematically applied to recover meaningful data, representing a significant compromise to network security policies that rely on ipsec for secure communications.
The vulnerability aligns with several common weakness enumerations including cwe-20, which covers improper input validation, and cwe-129, which addresses insufficient boundary checking. From an attack framework perspective, this vulnerability maps to techniques described in the attack tree methodology where attackers can exploit protocol implementation weaknesses to achieve information disclosure objectives. The attack vectors described in the cve entry correspond to specific tactics in the attack technique framework, particularly those involving packet manipulation and error message exploitation. Organizations implementing ipsec security solutions must understand that this vulnerability represents a failure in the protocol's defensive mechanisms rather than an issue with the cryptographic algorithms themselves.
Mitigation strategies for this vulnerability require immediate implementation of packet filtering rules that prevent malformed packets from reaching ipsec processing components. Network administrators should deploy ingress and egress filtering to block packets with suspicious header modifications, particularly those that attempt to manipulate ip header fields in ways that could trigger the vulnerability. System updates and patches should be applied immediately to address the underlying implementation flaws in ipsec processing code. Organizations should also implement monitoring solutions that can detect unusual patterns of icmp error message generation that might indicate exploitation attempts. The recommended approach includes both defensive measures to prevent exploitation and detection capabilities to identify potential attacks that may already be underway, ensuring comprehensive protection against this specific class of ipsec vulnerability that affects network security infrastructure.