CVE-2002-1831 in MSN Messenger
Summary
by MITRE
Microsoft MSN Messenger Service 1.0 through 4.6 allows remote attackers to cause a denial of service (crash) via an invite request that contains hex-encoded spaces (%20) in the Invitation-Cookie field.
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Analysis
by VulDB Data Team • 04/22/2025
The vulnerability described in CVE-2002-1831 represents a classic denial of service flaw affecting Microsoft MSN Messenger Service versions 1.0 through 4.6. This issue specifically targets the service component that handles invitation requests within the MSN Messenger ecosystem, creating a condition where malformed invitation cookies containing hex-encoded spaces can trigger system instability. The vulnerability operates at the application layer and demonstrates poor input validation mechanisms within the messenger service implementation.
The technical flaw manifests when the MSN Messenger Service processes invitation requests that contain hex-encoded spaces represented as %20 within the Invitation-Cookie field. This particular encoding pattern represents a common URL encoding technique that should be properly handled by the service. The service fails to adequately sanitize or validate these encoded characters, leading to a buffer overflow or memory corruption condition that ultimately causes the service to crash and become unavailable. This vulnerability falls under the category of improper input validation as classified by CWE-20, which specifically addresses weakness in input sanitization and validation processes.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides attackers with a straightforward method to render the MSN Messenger Service unusable for legitimate users. The remote exploitation nature of this flaw means that attackers can trigger the denial of service condition without requiring local access or elevated privileges, making it particularly dangerous in networked environments. When the service crashes, users lose connectivity to the messenger service, potentially disrupting communication channels that depend on MSN Messenger for business or personal correspondence. The vulnerability affects a broad range of versions, indicating that it was a persistent issue within the MSN Messenger Service architecture that required multiple patches to address properly.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and sanitization within the service components that handle invitation requests. System administrators should apply the appropriate security patches released by Microsoft to address this specific issue, as the vulnerability affects multiple versions of the service. Network-level protections can include implementing filtering rules that block malformed invitation requests or monitoring for unusual patterns in invitation cookie handling. The ATT&CK framework categorizes this type of vulnerability under privilege escalation and denial of service tactics, as it allows attackers to compromise service availability without requiring elevated system privileges. Organizations should also consider implementing network segmentation to limit the impact of such attacks and ensure that critical communication services maintain redundancy and failover capabilities to maintain operational continuity during potential exploitation attempts.