John Goerzen

A heap buffer overflow exists in the `putsrv()` function within the `ckcfns.c` file. This issue occurs when the software processes crafted packets, allowing malicious peers to write data beyond the `srvcmd` buffer. Specifically, attackers can leverage Kermit repeat-count compression in server command, GET, or file-header packets to write arbitrary bytes beyond the heap buffer on servers or receiving instances.

An OS command injection flaw allows remote clients to execute shell commands on the server host. This occurs when unquoted arguments are supplied to the 'REMOTE WHO' or 'REMOTE SPACE' endpoints. Attackers can append shell metacharacters to arguments passed through `WHOCMD` or `SPACM2` to the `syscmd()` function, bypassing the DISABLE HOST setting.

Remote code execution is possible on servers where host commands are disabled. This occurs by abusing REMOTE QUERY evaluation, allowing clients to execute shell commands. Attackers can achieve this by sending a REMOTE QUERY that invokes the `command` function or by defining a macro through REMOTE ASSIGN and calling `execute` to reach `RUN`, which bypasses the `nopush` restriction and `DISABLE HOST` setting.

The IKSD SSL build contains an issue where the Telnet authentication state remains at `AUTH VALID` after a certificate login is refused. This allows an attacker who possesses a trusted certificate mapped to a refused account to authenticate as any other account using any password, thereby gaining shell access to that account.

Improper certificate validation allows machine-in-the-middle attackers to impersonate Telnet servers. This occurs because the `ssl reply()` function fails to call `ssl check server name()`. An attacker can refuse START-TLS, offer Telnet AUTHENTICATION SSL, and present any trusted CA certificate to capture user credentials and session data.

C-Kermit 8.0.200 before 11.1.515 contains an improper certificate hostname validation vulnerability that allows attackers to impersonate hosts by abusing wildcard matching in dNSName cmp() in ck ssl.c. Attackers holding a trusted certificate with over-matching names containing asterisks, question marks, brackets, or empty labels can intercept credentials and data over Telnet, FTP, and HTTP TLS connections.

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/authorized keys or shell startup files under the current directory, which rq under root() accepts silently, enabling persistent access or code execution.

C-Kermit 8.0.200 before 11.1.515 contains a path traversal vulnerability in doftpget() in ckcftp.c that allows malicious FTP servers to write files outside the intended directory. Attackers can return absolute paths, tilde names, or dot-dot components in NLST or MLSD listings during MGET /RECURSIVE to overwrite files like .bashrc, leading to code execution.

C-Kermit 6.0.192 before 11.1.515 contains a buffer overflow vulnerability in tn snenv() 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 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 reply buf with attacker-controlled bytes.

A remote Kermit system can overwrite files on the local system or retrieve arbitrary files from the local system.

The issue is related to the improper creation of temporary files by gopher.c in the Gopher client, allowing local users to gain privileges.