CVE-2008-1897 in Asterisk
Summary
by MITRE
The IAX2 channel driver (chan_iax2) in Asterisk Open Source 1.0.x, 1.2.x before 1.2.28, and 1.4.x before 1.4.19.1; Business Edition A.x.x, B.x.x before B.2.5.2, and C.x.x before C.1.8.1; AsteriskNOW before 1.0.3; Appliance Developer Kit 0.x.x; and s800i before 1.1.0.3, when configured to allow unauthenticated calls, does not verify that an ACK response contains a call number matching the server s reply to a NEW message, which allows remote attackers to cause a denial of service (traffic amplification) via a spoofed ACK response that does not complete a 3-way handshake. NOTE: this issue exists because of an incomplete fix for CVE-2008-1923.
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Analysis
by VulDB Data Team • 02/27/2025
The vulnerability described in CVE-2008-1897 represents a critical flaw in the IAX2 channel driver implementation within various versions of Asterisk Open Source and related products. This issue specifically affects systems configured to accept unauthenticated calls, creating a pathway for remote attackers to exploit the protocol's handshake mechanism. The vulnerability stems from an incomplete remediation of a previously identified weakness, making it particularly concerning as it demonstrates the complexity of securing telephony protocols and the potential for flawed fixes to create new attack vectors.
The technical flaw manifests in the IAX2 protocol's handling of acknowledgment responses within the call establishment process. When a server responds to a NEW message with a call number, the system fails to validate that subsequent ACK responses contain matching call identifiers. This validation gap allows malicious actors to craft spoofed ACK messages that do not participate in the proper three-way handshake process. The protocol's design assumes that legitimate responses will maintain proper call number correlation, but this assumption breaks down when attackers can manipulate the call state through crafted responses.
The operational impact of this vulnerability extends beyond simple denial of service to include traffic amplification effects that can overwhelm network resources and system capabilities. Attackers can exploit this weakness to generate excessive traffic volumes by sending spoofed ACK responses that appear to be legitimate parts of call establishment but actually consume system resources without completing proper connection sequences. This creates a scenario where network bandwidth and processing capacity can be rapidly consumed, leading to service degradation or complete system unavailability for legitimate users.
Systems utilizing affected versions of Asterisk, including Business Edition products, AsteriskNOW, and various appliance configurations, face significant exposure when configured with unauthenticated call handling enabled. The vulnerability affects multiple release streams including 1.0.x, 1.2.x series before specific patches, and 1.4.x versions prior to designated updates. Organizations running these systems without proper authentication mechanisms or network segmentation are particularly vulnerable to exploitation, as the attack requires minimal privileges and can be executed remotely.
Mitigation strategies should focus on implementing proper call number validation within the IAX2 protocol handling, ensuring that all ACK responses contain matching call identifiers from the original NEW message. System administrators should immediately upgrade to patched versions of Asterisk software, particularly targeting the specific version numbers mentioned in the advisory. Network-level protections including firewall rules to restrict IAX2 traffic and implementing authentication requirements for call establishment can provide additional defense layers. The vulnerability aligns with CWE-284 access control weaknesses and can be mapped to ATT&CK technique T1498 for resource exhaustion attacks, emphasizing the importance of proper protocol validation and authentication mechanisms.
The incomplete fix referenced in the CVE description highlights the challenges of telephony protocol security and the need for comprehensive vulnerability analysis. This vulnerability demonstrates how security patches may not fully address underlying architectural flaws, requiring organizations to maintain vigilance and perform thorough testing of security updates. The remediation process should include not only software upgrades but also comprehensive testing of call handling procedures to ensure that the protocol's integrity is maintained throughout the communication process.