C-Kermit 8.0.200 before 11.1.515 contains an improper certificate validation vulnerability that allows machine-in-the-middle attackers to impersonate Telnet servers because sslreply() never calls sslcheckservername(). Attackers can refuse START-TLS, offer Telnet AUTHENTICATION SSL, and present any trusted CA certificate to capture user credentials and session data.

C-Kermit from 7.0.197 before 11.1.515 contains an authentication bypass vulnerability in the IKSD SSL build that leaves Telnet authentication state at AUTHVALID after a refused certificate login. Attackers holding a trusted certificate mapped to a refused account can log in as any other account with any password, gaining that account's shell access.

C-Kermit from 6.0.192 before 11.1.515 contains a file collision protection bypass that allows malicious senders to append data to existing files by marking transfers as RESEND. The gattr() function in ckcfn3.c clears the REJECT discard flag and switches to APPEND without a RECEIVE CONFIRM prompt, letting attackers modify files such as shell startup files.

C-Kermit 11.0.506 before 11.1.515 contains a RECEIVE CONFIRM bypass vulnerability that allows malicious Kermit servers to write unrequested files without prompting by abusing recursive GET root computation in ckcfns.c. Attackers can send files such as .ssh/authorizedkeys or shell startup files under the current directory, which rqunderroot() accepts silently, enabling persistent access or code execution.

C-Kermit 6.0.192 before 11.1.515 contains a buffer overflow vulnerability in tnsnenv() in ckctel.c that allows malicious Telnet servers to corrupt client memory via crafted NEW-ENVIRON SEND subnegotiation. Malicious or machine-in-the-middle servers can send oversized variable names before authentication, overflowing a 16-byte stack buffer and a miscomputed heap buffer to corrupt stack and heap memory.

C-Kermit before 11.1.515 contains an OS command injection vulnerability that allows remote clients to execute shell commands by supplying unquoted arguments to REMOTE WHO or REMOTE SPACE. Attackers can append shell metacharacters to arguments passed through WHOCMD or SPACM2 to syscmd(), executing commands on the server host even when DISABLE HOST is set.

C-Kermit 8.0.200 before 11.1.515 contains a buffer overflow vulnerability in getreply() in ckcftp.c that allows malicious FTP servers to overwrite client memory by sending overlong security replies. Attackers controlling or intercepting an FTP server can send long PBSZ replies after AUTH TLS, or long ADAT replies in GSSAPI, Kerberos 4, and SRP builds, overflowing the static replybuf with attacker-controlled bytes.

C-Kermit 6.0.192 before 11.1.515 contains a remote code execution vulnerability that allows Kermit clients to run shell commands on servers with host commands disabled by abusing REMOTE QUERY evaluation. Attackers can send a REMOTE QUERY invoking the command function, or define a macro via REMOTE ASSIGN and call execute to reach RUN, bypassing the nopush restriction and DISABLE HOST.

C-Kermit before 11.1.515 contains a heap buffer overflow vulnerability in putsrv() in ckcfns.c that allows malicious peers to write past the srvcmd buffer by sending crafted packets. Attackers can use Kermit repeat-count compression in server command, GET, or file-header packets to write attacker-chosen bytes beyond the heap buffer on servers or receiving instances.

The Session Initiation Protocol (SIP) implementation in Columbia SIP User Agent (sipc) 1.74 and other versions before sipc 2.0 build 2003-02-21 allows remote attackers to cause a denial of service or execute arbitrary code via crafted INVITE messages, as demonstrated by the OUSPG PROTOS c07-sip test suite.