CISCO has not only a long history of creating backdoors, but have also been marketing them as features. They even wrote an IETF proposal (RFC 2804) for a LI backdoor:
Edit: Schneier wrote in 2018: "We don't know if this is error or deliberate action, but five backdoors have been discovered [in CISCO] already this year." and linking to this article: https://www.tomshardware.com/news/cisco-backdoor-hardcoded-a... (the final count went up to 7 actual backdoors discovered in 2018.
https://tools.ietf.org/html/rfc2804
https://www.blackhat.com/presentations/bh-dc-10/Cross_Tom/Bl...
Edit: Schneier wrote in 2018: "We don't know if this is error or deliberate action, but five backdoors have been discovered [in CISCO] already this year." and linking to this article: https://www.tomshardware.com/news/cisco-backdoor-hardcoded-a... (the final count went up to 7 actual backdoors discovered in 2018.
From May 2019: https://www.scmagazineuk.com/cisco-firewalls-routers-switche...