CVE-2010-0577 in IOS
Summary
by MITRE
Cisco IOS 12.2 through 12.4, when certain PMTUD, SNAT, or window-size configurations are used, allows remote attackers to cause a denial of service (infinite loop, and device reload or hang) via a TCP segment with crafted options, aka Bug ID CSCsz75186.
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Analysis
by VulDB Data Team • 05/03/2026
Cisco IOS versions 12.2 through 12.4 contain a critical vulnerability in the TCP processing implementation that can be exploited to cause indefinite device reloads or system hangs. This vulnerability specifically manifests when certain Path Maximum Transmission Unit Discovery PMTUD, Source NAT SNAT, or window-size configuration parameters are active on the network device. The flaw occurs during the processing of TCP segments that contain crafted options, which triggers an infinite loop in the router's TCP stack implementation. This represents a classic denial of service condition where legitimate network traffic is disrupted through malicious packet construction. The vulnerability has been assigned the bug ID CSCsz75186 and demonstrates a fundamental flaw in how Cisco IOS handles TCP option parsing under specific network configuration scenarios.
The technical root cause of this vulnerability lies in the improper handling of TCP segment options within the IOS TCP stack when these specific configuration parameters are enabled. When a TCP segment containing specially crafted options is received, the processing routine enters an infinite loop that consumes system resources and eventually forces the device to reload or hang. This behavior aligns with CWE-835, which describes infinite loops in software implementations, and demonstrates how improper input validation can lead to system instability. The vulnerability is particularly concerning because it can be triggered remotely without authentication, making it a significant threat to network availability. The configuration parameters that enable this vulnerability include PMTUD which handles maximum packet size determination, SNAT which manages source network address translation, and window-size settings that control TCP flow control mechanisms.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise entire network infrastructure availability. Network administrators may experience unexpected device reboots that disrupt critical network services, leading to extended downtime and potential business disruption. The remote exploit capability means that attackers can trigger this condition from outside the network perimeter, making it particularly dangerous for internet-facing devices. This vulnerability affects a broad range of Cisco IOS versions and configurations, making it widespread across enterprise and service provider networks. The infinite loop condition can cause devices to become unresponsive, requiring manual intervention to restore normal operation. From an attacker perspective, this vulnerability maps to ATT&CK technique T1499.004 which involves network disruption through resource exhaustion and system instability.
Mitigation strategies for this vulnerability require immediate implementation of Cisco IOS patches and updates addressing the specific TCP processing flaw. Network administrators should disable the affected configuration parameters when possible, particularly PMTUD, SNAT, and window-size options that trigger the vulnerable code path. Implementing network access controls and filtering rules to drop malformed TCP segments can provide temporary protection while patches are deployed. The recommended approach includes applying the appropriate Cisco security advisory patches that address the TCP option processing logic. Organizations should also consider implementing monitoring solutions to detect unusual device behavior patterns that may indicate exploitation attempts. Regular vulnerability assessments and network configuration reviews are essential to prevent similar issues in other network infrastructure components. The vulnerability underscores the importance of maintaining current security patches and following secure configuration practices for network devices.