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Cisco Bug: CSCsz70906 - IPsec/TCP fails due to corrupt SYN+ACK from ASA when SYN has TCP options

Last Modified

Nov 09, 2016

Products (1)

  • Cisco ASA 5500-X Series Firewalls

Known Affected Releases

8.0(4.162) 8.0(4.27) 8.1(2.165)

Description (partial)


Cisco VPN client is unable to connect to PIX/ASA using IPsec over TCP from some locations.
Plain IPsec, IPsec with NAT-T, and IPsec over UDP are not affected.


VPN client and PIX/ASA are configured for IPsec over TCP, and a device in between is modifying the TCP SYN packet from the client by inserting the MSS option in the TCP header.
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